6,7-DIHYDROPYRAZOLO[1,5-a]PYRAZINONE DERIVATIVE AND MEDICAL USE THEREOF

ABSTRACT

Provided are a compound that is useful for the prevention of and/or as a treatment agent for a disease in which a group II mGlu receptor is involved; and a medical application of said compound. Provided is a compound represented by formula (I) or a pharmaceutically acceptable salt thereof.

TECHNICAL FIELD

The present invention relates to a 6,7-dihydropyrazolo[1,5-a]pyrazinonederivative, or a pharmaceutically acceptable salt thereof, havingnegative allosteric modulation against Group II metabotropic glutamate(mGlu) receptors, and a preventive and/or therapeutic agent for adisease involving metabotropic glutamate receptor subtype 2 (mGluR2)and/or metabotropic glutamate receptor subtype 3 (mGluR3), comprisingthe same as an active ingredient.

BACKGROUND ART

Glutamate is a major excitatory neurotransmitter in the central nervoussystem, and acts on ion-channel receptors (i.e., N-methyl-D-aspartate(NMDA) glutamate receptor,α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor,and kainate receptor) and G-protein-coupled receptors (GPCRs) such asmetabotropic glutamate receptors (mGlu receptors). mGlu receptors areclassified as class C of GPCRs, and have an extracellular largeorthosteric ligand binding site besides the seven transmembrane domain(TMD) common to GPCRs. mGlu receptors have high homology in theorthosteric ligand binding site, and it has been regarded as beingdifficult to develop subtype-selective orthosteric ligands. Allostericmodulators show the subtype selectivity by binding to the TMD (NonPatent Literatures 1 to 3).

mGlu receptors include 8 subtypes 1 to 8 (mGluR1 to 8), and areclassified into Group I (mGluR1, mGluR5), Group II (mGluR2, mGluR3), andGroup III (mGluR4, mGluR6, mGluR7, mGluR8) based on the homology, thesignaling system to be conjugated, and pharmacological properties. GroupII mGlu receptors (mGluR2, mGluR3) mainly express in presynapse, andnegatively modulate glutamate release. It has been, therefore, reportedthat mGlu2/3 receptor negative allosteric modulators (NAMs) have thepotential to an antidepressant (Non Patent Literature 4) andcognitive-function enhancer (Non Patent Literature 5).

Recently, compounds that act as an mGlu2/3 receptor NAM have beenreported in Patent Literatures 1 to 7. These patent literatures,however, do not disclose or indicate a compound of Formula (1) asdescribed hereinafter.

CITATION LIST Patent Literature

-   [Patent Literature 1] WO 2014/195311-   [Patent Literature 2] WO 2016/016380-   [Patent Literature 3] WO 2016/016381-   [Patent Literature 4] WO 2016/016382-   [Patent Literature 5] WO 2016/016383-   [Patent Literature 6] WO 2016/016395-   [Patent Literature 7] WO 2016/087487

Non Patent Literature

-   [Non Patent Literature 1]Hemstapat et al, Pharmacology and    Experimental Therapeutics, 2007, 322, 254-264-   [Non Patent Literature 2]Lungstrom et al, British Journal of    Pharmacology, 2011, 164, 521-537-   [Non Patent Literature 3]Dore et al, Nature, 2014, 511, 557-562-   [Non Patent Literature 4]Chaki et al, Neuropharmacology, 2013, 66,    40-52-   [Non Patent Literature 5]Higgins et al, Neuropharmacology, 2004, 46,    907-917

SUMMARY OF INVENTION Problems to be Solved by the Invention

A problem to be solved by the present invention is to find out novelcompounds having negative allosteric modulation against Group II mGlureceptors, and to provide a preventive and/or therapeutic agent usefulfor the treatment of a disease involving Group II mGlu receptors (i.e.,metabotropic glutamate receptor subtype 2 (mGluR2) and/or metabotropicglutamate receptor subtype 3 (mGluR3)).

Means of Solving the Problems

The present inventor has found out that the problem is solved by acompound of Formula (1) as described below, or a pharmaceuticallyacceptable salt thereof, also referred to as “the present compound”hereinafter, and has achieved the present invention.

The present invention includes the following embodiments.

[Item 1]

A compound of Formula (1):

or a pharmaceutically acceptable salt thereof,

wherein R¹ and R² are each independently hydrogen atom, halogen atom,cyano, C₁₋₄ alkyl, or C₃₋₆ saturated carbocyclyl group, wherein thealkyl and the saturated carbocyclyl group are each independent and maybe optionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy, or

alternatively, R¹ and R² may combine together with the carbon atom towhich they attach to form a C₃₋₄ saturated carbocyclyl group, whereinthe saturated carbocyclyl group may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy;

Ring A is C₆₋₁₀ aromatic carbocyclyl group, 4- to 10-membered saturatedheterocyclyl group, or 5- to 10-membered aromatic heterocyclyl group;

R³ and R⁴ are each independently hydrogen atom, halogen atom, cyano,hydroxy, C₁₋₆ alkyl, C₁₋₄ alkoxy, C₁₋₄ alkylthio, C₂₋₄ alkenyl, 4- to6-membered saturated heterocyclyl group, or 5- or 6-membered aromaticheterocyclyl group (wherein the alkyl, the alkoxy, the alkylthio, thesaturated heterocyclyl group, and the aromatic heterocyclyl group areeach independent and may be optionally substituted with the same ordifferent 1 to 5 halogen atoms), C₃₋₆ saturated carbocyclyl group, orC₃₋₆ cycloalkoxy, wherein the saturated carbocyclyl group and thecycloalkoxy are each independent and may be optionally substituted withthe same or different 1 to 5 substituents selected from the groupconsisting of halogen atom and C₁₋₄ alkyl;

R⁵ and R⁶ are each independently hydrogen atom, halogen atom, cyano,hydroxy, C₁₋₆ alkyl, C₁₋₆ alkoxy, C₁₋₆ alkylthio, 4- to 6-memberedsaturated heterocyclyl group (wherein the alkyl, the alkoxy, thealkylthio, and the saturated heterocyclyl group are each independent andmay be optionally substituted with the same or different 1 to 5substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy optionally substituted with the same ordifferent 1 to 5 halogen atoms), C₃₋₆ cycloalkoxy, C₃₋₆ saturatedcarbocyclyl group (wherein the cycloalkoxy and the saturated carbocyclylgroup are each independent and may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms),—NR^(a)R^(b), —NR^(d)—C(O)—R^(c), —NR^(d)—C(O)—OR^(c),—NR^(d)—C(O)—NR^(a)R^(b), —NR^(d)—SO₂—R^(c), —CH₂—C(O)—NR^(a)R^(b),—C(O)—R^(d), —C(O)—OR^(d), or —C(O)—NR^(a)R^(b);

R^(a) and R^(b) are each independent and R^(a)s or R^(b)s whenNR^(a)R^(b) exists plurally are each independent, and they are hydrogenatom, C₁₋₄ alkyl (wherein the alkyl is each independent and may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy), C₃₋₆ saturated carbocyclyl group, or 4- to 6-membered saturatedheterocyclyl group, wherein the saturated carbocyclyl group and thesaturated heterocyclyl group are each independent and may be optionallysubstituted with the same or different 1 to 5 substituents selected fromthe group consisting of halogen atom, hydroxy, C₁₋₄ alkyl, and C₁alkoxy, or

alternatively, R^(a) and R^(b) may combine together with the nitrogenatom to which they attach to form a 4- to 6-membered nitrogen-containingsaturated heterocyclyl group, wherein the nitrogen-containing saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄ alkoxy;

R^(c), where R^(c)s are each independent when existing plurally, is C₁₋₄alkyl, C₃₋₆ saturated carbocyclyl group, or 4- to 6-membered saturatedheterocyclyl group, wherein the alkyl, the saturated carbocyclyl group,and the saturated heterocyclyl group are each independent and may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy;

R^(d), where R^(d)s are each independent when existing plurally, ishydrogen atom, C₁₋₄ alkyl, C₃₋₆ saturated carbocyclyl group, or 4- to6-membered saturated heterocyclyl group, wherein the alkyl, thesaturated carbocyclyl group, and the saturated heterocyclyl group areeach independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy;

X is nitrogen atom or —CR^(e)—; and

R^(e) is hydrogen atom, halogen atom, cyano, C₁₋₆ alkyl, or C₁₋₆ alkoxy,wherein the alkyl and the alkoxy may be optionally substituted with thesame or different 1 to 5 halogen atoms.

[Item 2]

The compound according to Item 1, or a pharmaceutically acceptable saltthereof, wherein R¹ and R² are each independently hydrogen atom or C₁₋₄alkyl, wherein the alkyl may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy, or alternatively, R¹ and R²combine together with the carbon atom to which they attach to form acyclopropane ring or cyclobutane ring.

[Item 3]

The compound according to Item 1 or 2, or a pharmaceutically acceptablesalt thereof, wherein Ring A is benzene, naphthalene, pyridine,pyrimidine, pyrazine, thiophene, thiazole, isothiazole, oxazole,isoxazole, quinoline, isoquinoline, benzothiophene, benzofuran,indolizine, imidazopyridine, 1,3-benzodioxole, chromane,2,3-dihydrobenzofuran, 1,3-dihydroisobenzofuran, 2,3-dihydro-1H-indene,or 2,3-dihydro-1H-inden-1-one.

[Item 4]

The compound according to any one of Items 1 to 3, or a pharmaceuticallyacceptable salt thereof, wherein R³ and R⁴ are each independently

(1) hydrogen atom,(2) halogen atom,(3) cyano,(4) hydroxy,(5) C₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms,(6) C₁₋₄ alkoxy optionally substituted with the same or different 1 to 5halogen atoms,(7) C₃₋₆ cycloalkoxy, wherein the cycloalkoxy may be optionallysubstituted with the same or different 1 to 5 substituents selected fromthe group consisting of C₁₋₄ alkyl and halogen atom, or(8) C₁₋₄ alkylthio optionally substituted with the same or different 1to 5 halogen atoms.

[Item 5]

The compound according to any one of Items 1 to 4, or a pharmaceuticallyacceptable salt thereof, wherein R⁵ and R⁶ are each independently

(1) hydrogen atom,(2) halogen atom,(3) cyano,(4) hydroxy,(5) C₁₋₄ alkyl, wherein the alkyl may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted withthe same or different 1 to 5 halogen atoms,(6) C₁ alkoxy, wherein the alkoxy may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted withthe same or different 1 to 5 halogen atoms,(7) 4- to 6-membered saturated heterocyclyl group, wherein the saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, or(8)—NR^(a)R^(b), —NR^(d)—C(O)—R^(c), —NR^(d)—C(O)—OR^(c),—NR^(d)—C(O)—NR^(a)R^(b), —NR^(d)—SO₂—R^(c), —CH₂—C(O)—NR^(a)R^(b),—C(O)—R^(d), —C(O)—OR^(d), or —C(O)—NR^(a)R^(b).

[Item 6]

The compound according to any one of Items 1 to 5, or a pharmaceuticallyacceptable salt thereof, wherein R^(a) and R^(b) are each independentand R^(a)s or R^(b)s when NR^(a)R^(b) exists plurally are eachindependent, and they are hydrogen atom or C₁₋₄ alkyl, wherein the alkylis each independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy, or alternatively, R^(a) andR^(b) combine together with the nitrogen atom to which they attach toform a 4- to 6-membered nitrogen-containing saturated heterocyclylgroup, wherein the nitrogen-containing saturated heterocyclyl group maybe optionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, C₁₋₄ alkyl,and C₁₋₄ alkoxy.

[Item 7]

The compound according to any one of Items 1 to 6, or a pharmaceuticallyacceptable salt thereof, wherein R^(c), where R^(c)s are eachindependent when existing plurally, is C₁₋₄ alkyl or C₃₋₆ saturatedcarbocyclyl group, wherein the alkyl and the saturated carbocyclyl groupare each independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy.

[Item 8]

The compound according to any one of Items 1 to 7, or a pharmaceuticallyacceptable salt thereof, wherein R^(d), where R^(d)s are eachindependent when existing plurally, is

(1) hydrogen atom,(2) C₁₋₄ alkyl, wherein the alkyl may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy, or(3) C₃₋₆ saturated carbocyclyl group, wherein the saturated carbocyclylgroup may be optionally substituted with the same or different 1 to 5substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy.

[Item 9]

The compound according to any one of Items 1 to 8, or a pharmaceuticallyacceptable salt thereof, wherein R^(e) is

(1) hydrogen atom,(2) halogen atom, or(3) C₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms.

[Item 10]

The compound according to any one of Items 1, 3 to 9, or apharmaceutically acceptable salt thereof, wherein R¹ and R² are eachindependently hydrogen atom, methyl, ethyl, isopropyl, cyclopropyl,methoxymethyl, hydroxymethyl, difluoromethyl, or trifluoromethyl, oralternatively, R¹ and R² combine together with the carbon atom to whichthey attach to form a cyclopropane ring or a cyclobutane ring.

[Item 11]

The compound according to any one of Items 1 to 10, or apharmaceutically acceptable salt thereof, wherein Ring A is benzene,thiophene, pyridine, quinoline, or 1,3-benzodioxole.

[Item 12]

The compound according to any one of Items 1 to 11, or apharmaceutically acceptable salt thereof, wherein R³ and R⁴ are eachindependently

(1) hydrogen atom,(2) halogen atom,(3) cyano,(4) C₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms, or(5) C₁₋₄ alkoxy optionally substituted with the same or different 1 to 5halogen atoms.

[Item 13]

The compound according to any one of Items 1 to 12, or apharmaceutically acceptable salt thereof, wherein R^(c), where R^(c)sare each independent when existing plurally, is C₁₋₄ alkyl optionallysubstituted with the same or different 1 to 5 halogen atoms.

[Item 14]

The compound according to any one of Items 1 to 13, or apharmaceutically acceptable salt thereof, wherein R^(d), where R^(d)sare each independent when existing plurally, is hydrogen atom or C₁₋₄alkyl optionally substituted with the same or different 1 to 5 halogenatoms.

[Item 15]

The compound according to any one of Items 1 to 14, or apharmaceutically acceptable salt thereof, wherein R⁵ and R⁶ are eachindependently

(1) hydrogen atom,(2) halogen atom,(3) cyano,(4) hydroxy,(5) C₁₋₄ alkyl, wherein the alkyl may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted withthe same or different 1 to 5 halogen atoms,(6) C₁₋₄ alkoxy, wherein the alkoxy may be optionally substituted withthe same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms,(7) 4- to 6-membered saturated heterocyclyl group, wherein the saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, or(8)—NR^(a)R^(b).

[Item 16]

The compound according to any one of Items 1 to 15, or apharmaceutically acceptable salt thereof, wherein R^(a) and R^(b) areeach independent and R^(a)s or R^(b)s when NR^(a)R^(b) exists plurallyare each independent, and they are hydrogen atom or C₁₋₄ alkyl, whereinthe alkyl may be optionally substituted with the same or different 1 to3 substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy.

[Item 17]

The compound according to any one of Items 1 to 16, or apharmaceutically acceptable salt thereof, wherein R^(e) is

(1) hydrogen atom,(2) fluorine atom, or(3) C₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms.

[Item 18]

The compound according to Item 1, or a pharmaceutically acceptable saltthereof, wherein R¹ is methyl;

R² is hydrogen atom;

a 6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one moiety has S-configurationat the 7-position;

Ring A is benzene;

R³ and R⁴ are each independently hydrogen atom, fluorine, chlorine,difluoromethyl, trifluoromethyl, or difluoromethoxy;

R⁵ and R⁶ are each independently hydrogen atom or —NH₂; and

X is nitrogen atom or —CH—.

[Item 19]

The compound according to Item 1, or a pharmaceutically acceptable saltthereof, selected from the following compounds:

-   Example 1:    (7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 2:    (7S)-3-(imidazo[1,2-a]pyrazin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 3:    (7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[3-chloro-4-fluorophenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 4:    (7S)-5-[4-(difluoromethyl)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 5:    (7S)-5-(4-chloro-3-fluorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 6:    (7S)-5-(4-chlorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 9:    (7S)-5-[4-(difluoromethoxy)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;    and-   Example 11:    (7S)-3-(3-aminoimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one.

[Item 20]

The compound according to Item 1, or a pharmaceutically acceptable saltthereof, selected from the following compounds:

-   Example 13:    (7S)-3-(3-fluoroimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 14:    (7S)-7-methyl-3-(3-methylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 15:    (7S)-3-(3-ethylimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;    and-   Example 16:    (7S)-7-methyl-3-(3-propylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one.

[Item 21]

The compound according to Item 1, or a hydrochloride or phosphate saltthereof, selected from the following compounds:

-   Example 1:    (7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 3:    (7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[3-chloro-4-fluorophenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;-   Example 13:    (7S)-3-(3-fluoroimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;    and-   Example 14:    (7S)-7-methyl-3-(3-methylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one.

[Item 22]

A pharmaceutical composition comprising a compound according to any oneof Items 1 to 21, or a pharmaceutically acceptable salt thereof.

[Item 23]

A therapeutic agent and/or preventive agent for a disease involvingGroup II mGlu receptor, comprising a compound according to any one ofItems 1 to 21, or a pharmaceutically acceptable salt thereof, as anactive ingredient.

[Item 24]

The therapeutic agent and/or preventive agent according to Item 23,wherein the Group II mGlu receptor is metabotropic glutamate receptorsubtype 2 (mGluR2).

[Item 25]

The therapeutic agent and/or preventive agent according to Item 23 or24, wherein the disease involving Group II mGlu receptor is psychiatricdisease or neurodegenerative disease.

[Item 26]

The therapeutic agent and/or preventive agent according to Item 25,wherein the psychiatric disease or neurodegenerative disease is majordepressive disorder, depressive disorder, bipolar and related disorders,anxiety disorder, posttraumatic stress disorder, obsessive-compulsivedisorder, acute stress disorder, schizophrenia, autism spectrumdisorder, Alzheimer's disease, cognitive dysfunction, dementia, drugdependence, obesity, seizure, tremor, pain, or sleep disorder.

[Item 27]

Use of a compound according to any one of Items 1 to 21, or apharmaceutically acceptable salt thereof, in the manufacture of atherapeutic agent and/or preventive agent for a disease involving GroupII mGlu receptor.

[Item 28]

A compound according to any one of Items 1 to 21, or a pharmaceuticallyacceptable salt thereof, for use in the treatment and/or prevention of adisease involving Group II mGlu receptor.

[Item 29]

A method for treating and/or preventing a disease involving Group IImGlu receptor, comprising administering a therapeutically effectiveamount of a compound according to any one of Items 1 to 21, or apharmaceutically acceptable salt thereof, to a patient in need thereof.

[Item 30]

A medicament which comprises a medicament comprising a compoundaccording to any one of Items 1 to 21, or a pharmaceutically acceptablesalt thereof, and one or more medicaments selected from therapeuticagents for major depressive disorder, depressive disorder, bipolar andrelated disorders, anxiety disorder, posttraumatic stress disorder,obsessive-compulsive disorder, acute stress disorder, schizophrenia,autism spectrum disorder, Alzheimer's disease, cognitive dysfunction,dementia, drug dependence, obesity, seizure, tremor, pain, or sleepdisorder.

[Item 31]

A medicament for treating psychiatric disease or neurodegenerativedisease, comprising a compound according to any one of Items 1 to 21, ora pharmaceutically acceptable salt thereof, for use in combination withone or more antipsychotic drugs.

[Item 32]

A method of preparing a compound of Formula (1a):

or a pharmaceutically acceptable salt thereof,

wherein R³ and R⁴ are each independently hydrogen atom, halogen atom,C₁₋₆ alkyl, or C₁₋₄ alkoxy, wherein the alkyl and the alkoxy are eachindependent and may be optionally substituted with the same or different1 to 5 halogen atoms;

R⁵ and R⁶ are each independently hydrogen atom, halogen atom, C₁₋₆alkyl, or —NH₂; and

X is nitrogen atom or —CH—,

which comprises the following steps:

(step A1) reacting a compound of Formula (4a):

wherein PG is a protecting group such as tert-butoxycarbonyl group andbenzyloxycarbonyl group, and a compound of Formula (3):

wherein R⁷ is methyl or ethyl,

under Mitsunobu condition to give a compound of Formula (6a):

wherein PG and R⁷ are as defined in this Item; (step A2) cyclizing thecompound of Formula (6a) in the presence of an acid or base to give acompound of Formula (7a):

(step A3) coupling the compound of Formula (7a) and a compound ofFormula (8a):

wherein R³ and R⁴ are as defined in this Item, and X¹ is iodine,bromine, or chlorine,

in the presence of a transition metal catalyst to give a compound ofFormula (9a)

wherein R³ and R⁴ are as defined in this Item;

(step A4) reacting the compound of Formula (9a) in the presence of ahalogenating agent to give a compound of Formula (15a)

wherein R³, R⁴, and X¹ are as defined in this Item; and

(step A5) coupling the compound of Formula (15a) and a compound ofFormula (16):

or a salt thereof,

wherein R⁵, R⁶, and X are as defined in this claim, and R^(A) is boronicacid or boronic acid ester,

in the presence of a transition metal catalyst to give a compound ofFormula (1a) or a pharmaceutically acceptable salt thereof.

[Item 33]

A method of preparing a compound of Formula (1a):

or a pharmaceutically acceptable salt thereof,

wherein R³ and R⁴ are each independently hydrogen atom, halogen atom,C₁₋₆ alkyl, or C₁₋₄ alkoxy, wherein the alkyl and the alkoxy are eachindependent and may be optionally substituted with the same or different1 to 5 halogen atoms;

R⁵ and R⁶ are each independently hydrogen atom, halogen atom, C₁₋₆alkyl, or —NH₂; and

X is nitrogen atom or —CH—,

which comprises the following steps:

(step B1) coupling a compound of Formula (8a):

wherein R³ and R⁴ are as defined in this Item, and X¹ is iodine,bromine, or chlorine,

with a compound of Formula (12a):

or a salt thereof,in the presence of a transition metal catalyst to give a compound ofFormula (13a):

or a salt thereof,

wherein R³ and R⁴ are as defined in this Item;

(step B2) reacting the compound of Formula (13a), or a salt thereof, anda compound of Formula (22):

or a salt thereof,

wherein X¹ is as defined in this Item, and R⁷ is methyl or ethyl,

under Mitsunobu condition to give a compound of Formula (23a):

or a salt thereof,

wherein R³, R⁴, R⁷, and X¹ are as defined in this Item;

(step B3) hydrolyzing the compound of Formula (23a), or a salt thereof,in the presence of an acid or base to give a compound of Formula (24a):

or a salt thereof,

wherein R³, R⁴, and X¹ are as defined in this Item;

(step B4) cyclizing the compound of Formula (24a), or a salt thereof, inthe presence of an acid or base to give a compound of Formula (15a):

wherein R³, R⁴, and X¹ are as defined in this Item; and

(step B5) coupling the compound of Formula (15a) and a compound ofFormula (16):

or a salt thereof,

wherein R⁵, R⁶, and X are as defined in this Item, and R^(A) is boronicacid or boronic acid ester,

in the presence of a transition metal catalyst to give a compound ofFormula (1a), or a pharmaceutically acceptable salt thereof;

wherein the step B3 and step B4 may be replaced with one single step ofthe following step B6:

(step B6) cyclizing the compound of Formula (23a), or a salt thereof, inthe presence of an acid or base to give a compound of Formula (15a).

[Item 34]

A crystal (Crystalline Form I) of(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one,having a powder X-ray diffraction pattern comprising diffraction peaksat diffraction angles 2θ (°): 4.5±0.2, 8.5±0.2, 8.9±0.2, 10.1±0.2,13.4±0.2, and 16.9±0.2, measured by powder X-ray diffraction.

[Item 35]

A crystal (Crystalline Form II) of a hydrochloride salt of(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one,having a powder X-ray diffraction pattern comprising diffraction peaksat diffraction angles 2θ (°): 5.7±0.2, 8.7±0.2, 9.5±0.2, 11.0±0.2,11.3±0.2, and 15.3±0.2, measured by powder X-ray diffraction.

[Item 36]

A crystal (Crystalline Form III) of a 2.5 phosphate salt of(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one,having a powder X-ray diffraction pattern comprising diffraction peaksat diffraction angles 2θ (°): 6.1±0.2, 8.9±0.2, 9.8±0.2, 12.1±0.2,13.4±0.2, and 13.7±0.2, measured by powder X-ray diffraction.

Effect of the Invention

The present compound shows negative allosteric modulation against GroupII metabotropic glutamate (mGlu) receptors. Thus, the present compoundis useful for a therapeutic agent and/or preventive agent for a diseaseinvolving Group II mGlu receptors (i.e., metabotropic glutamate receptorsubtype 2 (mGluR2) and/or metabotropic glutamate receptor subtype 3(mGluR3)).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a powder X-ray diffraction pattern of Crystalline Form I.The horizontal axis indicates diffraction angles 2θ (°), whereas thevertical axis indicates the number of counts; hereinafter, the same canbe applied to FIGS. 2 and 3.

FIG. 2 shows a powder X-ray diffraction pattern of Crystalline Form II.

FIG. 3 shows a powder X-ray diffraction pattern of Crystalline Form III.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the terms used herein are explained.

The term “group” means a monovalent group. The term “group” may beomitted herein.

The number of substituents in a group defined with the term “optionallysubstituted” or “substituted” is not limited as long as they areapplicable. Each definition of each group is also applicable to the casewhere the group is a part or a substituent of other groups, unlessotherwise indicated.

The term “C₁₋₄ alkyl” means an aliphatic hydrocarbon group having 1 to 4carbon atoms, and the term “C_(G) alkyl” means an aliphatic hydrocarbongroup having 4 carbon atoms. The same can be applied to the othernumbers. Examples of “C₁₋₄ alkyl” include, for example, methyl, ethyl,n-propyl, 1-methylethyl, n-butyl, 1,1-dimethylethyl, 1-methylpropyl, and2-methylpropyl.

The term “C₁₋₆ alkyl” means an aliphatic hydrocarbon group having 1 to 6carbon atoms. “C₁₋₆ alkyl” includes, preferably, “C₁₋₄ alkyl”. Examplesof “C₁₋₆ alkyl” include, for example, 4-methylpentyl, 3-methylpentyl,2-methylpentyl, 1-methylpentyl, and n-hexyl besides the examples of“C₁₋₄ alkyl” as described above.

The term “halogen” includes, for example, fluorine, chlorine, bromine,and iodine. A preferable one is fluorine or chlorine.

The term “C₁₋₄ alkoxy” means an oxy group substituted with “C₁₋₄ alkyl”as described above. Examples of “C₁₋₄ alkoxy” include, for example,methoxy, ethoxy, n-propoxy, 1-methylethoxy, n-butoxy,1,1-dimethylethoxy, 1-methylpropoxy, and 2-methylpropoxy. A preferableone is methoxy or ethoxy.

The term “C₁₋₆ alkoxy” means an oxy group substituted with “C₁₋₆ alkyl”as described above. “C₁₋₆ alkoxy” includes, preferably, “C₁₋₄ alkoxy”.Examples of “C₁₋₆ alkoxy” include, for example, n-pentyloxy,3-methylbutoxy, 2-methylbutoxy, 2,2-dimethylpropoxy, 1-ethylpropoxy,1,1-dimethylpropoxy, n-hexyloxy, 4-methylpentyloxy, 3-methylpentyloxy,2-methylpentyloxy, 1-methylpentyloxy, 3,3-dimethylbutoxy,2,2-dimethylbutoxy, 1,1-dimethylbutoxy, and 1,2-dimethylbutoxy besidesthe examples of “C₁₋₄ alkoxy” as described above.

The term “C₃₋₆ cycloalkoxy” means an oxy group substituted with cyclicalkyl having 3 to 6 carbon atoms.

Examples of “C₃₋₆ cycloalkoxy” include, for example, cyclopropoxy,cyclobutoxy, cyclopentyloxy, and cyclohexyloxy. A preferable one iscyclopropoxy or cyclobutoxy.

The term “C₁₋₄ alkylthio” means a thiol group substituted with “C₁₋₄alkyl” as described above. Examples of “C₁₋₄ alkylthio” include, forexample, methylthio, ethylthio, n-propylthio, isopropylthio,n-butylthio, isobutylthio, s-butylthio, and t-butylthio.

The term “C>₆ alkylthio” means a thiol group substituted with “C₁₋₆alkyl” as described above. “C₁₋₆ alkylthio” includes, preferably, “C₁₋₄alkylthio”. Examples of “C₁₋₆ alkylthio” include, for example,1-ethylpropylthio, n-pentylthio, neopentylthio, n-hexylthio, andisohexylthio besides the examples of “C₁₋₄ alkylthio” as describedabove.

The term “C₂₋₄ alkenyl” means an aliphatic hydrocarbon group having 2 to4 carbon atoms in the chain and comprising at least one carbon-carbondouble bond. Examples of “C₂₋₄ alkenyl” include, for example, vinyl,allyl, 1-propenyl, and 1-butenyl.

The term “C₃₋₆ saturated carbocycle” means a monocyclic saturated orpartially unsaturated hydrocarbon ring having 3 to 6 carbon atoms. “C₃₋₆saturated carbocycle” includes, preferably, “C₃₋₄ saturated carbocycle”.Examples of “C₃₋₆ saturated carbocycle” include, for example,cyclopropane, cyclobutane, cyclopentane, cyclohexane, cyclopropene,cyclobutene, cyclopentene, cyclohexene, and cyclohexadiene. A preferableone is cyclopropane or cyclobutane.

The term “C₃₋₄ saturated carbocyclyl group” means a monovalent group of“C₃₋₄ saturated carbocycle” among “C₃₋₆ saturated carbocycle” asdescribed above.

The term “4- to 10-membered saturated heterocycle” means a monocyclic orbicyclic saturated heterocycle consisting of 4 to 10 atoms, comprisingthe same or different one or two heteroatoms selected from the groupconsisting of oxygen atom, nitrogen atom, and sulfur atom, and includesthat which comprises a partially unsaturated bond, partially bridgedstructure, or partial spiro structure. The bicyclic saturatedheterocycle includes a fused ring wherein a monocyclic saturatedheterocycle is fused with benzene or a monocyclic 5- to 6-memberedaromatic heterocycle. The saturated heterocycle may comprise one or twocarbonyl, thiocarbonyl, sulfinyl, or sulfonyl for formation, andincludes cyclic groups such as lactam, thiolactam, lactone, thiolactone,cyclic imide, cyclic carbamate, and cyclic thiocarbamate. The oxygenatom of carbonyl, sulfinyl, and sulfonyl or the sulfur atom ofthiocarbonyl is not counted as the number of the 4- to 10-members (i.e.,the size of the ring) or heteroatoms that form the ring. The “4- to10-membered saturated heterocycle” includes, preferably a monocyclic orbicyclic “4- to 8-membered saturated heterocycle”, more preferably amonocyclic “4- to 6-membered saturated heterocycle”, further preferablya monocyclic “5- or 6-membered saturated heterocycle”. Examples of the“4- to 10-membered saturated heterocycle” include, for example,azetidine, pyrrolidine, piperidine, piperazine, morpholine,homopiperidine, oxetane, tetrahydrofuran, tetrahydropyran,1,3-benzodioxole, and 1,3-dihydroisobenzofuran, and preferably,pyrrolidine, piperidine, piperazine, morpholine, 1,3-benzodioxole, and1,3-dihydroisobenzofuran.

The term “4- to 6-membered saturated heterocyclyl group” means amonovalent group of “4- to 6-membered saturated heterocycle” among “4-to 10-membered saturated heterocycle” as described above. A preferableone is azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, morpholinyl,oxetanyl, tetrahydrofuranyl, or tetrahydropyranyl.

The term “4- to 6-membered nitrogen-containing saturated heterocyclylgroup” means a monovalent saturated heterocyclyl group comprising atleast one nitrogen atom among “4- to 6-membered saturated heterocycle”as described above. A preferable one is azetidinyl, pyrrolidinyl,piperidinyl, piperazinyl, or morpholinyl.

The term “C₆₋₁₀ aromatic carbocycle” means a monocyclic or bicyclicaromatic hydrocarbon ring having 6 to 10 carbon atoms. Examples of“C₆₋₁₀ aromatic carbocycle” include, for example, benzene,1-naphthalene, and 2-naphthalene, and preferably benzene.

The term “5- to 10-membered aromatic heterocycle” means a monocyclic orbicyclic aromatic heterocycle consisting of 5 to 10 atoms, comprisingthe same or different 1 to 3 heteroatoms selected from the groupconsisting of oxygen atom, nitrogen atom, and sulfur atom. The “5- to10-membered aromatic heterocycle” includes, preferably a monocyclic orbicyclic “5- to 9-membered aromatic heterocycle”, more preferably amonocyclic “5- to 8-membered aromatic heterocycle”, further preferably amonocyclic “5- or 6-membered aromatic heterocycle”. Examples of “5- to10-membered aromatic heterocycle” include, for example, pyridine,pyridazine, pyrimidine, pyrazine, triazine, thiophene, pyrrole,thiazole, isothiazole, pyrazole, imidazole, furan, oxazole, isoxazole,oxadiazole, thiadiazole, triazole, tetrazole, quinoline, isoquinoline,naphthyridine, quinazoline, benzofuran, benzothiophene, indole,benzoxazole, benzoisoxazole, 1H-indazole, 2H-indazole, benzimidazole,benzoxadiazole, benzothiadiazole, indolizine, benzofurazine,thienopyrimidine, pyrazolopyridine, imidazopyridine, imidazopyrazine,pyrazolopyrimidine, triazolopyrimidine, thienothiophene,imidazothiazole, chromane, 2,3-dihydrobenzofuran, 1,3-dihydrobenzofuran,2,3-dihydro-1H-indene, 2,3-dihydro-1H-inden-1-one,2,3-dihydro-1-1H-pyrrolopyridine, 2,3-dihydro-1H-pyrrolopyridin-1-one,1,2-dihydro-3H-pyrrolopyridin-3-one, and5,6,7,8-tetrahydroimidazopyrazine.

The “5-membered aromatic heterocycle” includes, for example, thiophene,pyrrole, thiazole, isothiazole, pyrazole, imidazole, furan, oxazole,isoxazole, oxadiazole, thiadiazole, triazole, and tetrazole. Apreferable one includes thiophene, thiazole, and isothiazole.

The “6-membered aromatic heterocycle” includes, for example, pyridine,pyridazine, pyrimidine, and pyrazine. A preferable one is pyridine.

The term “5- or 6-membered aromatic heterocyclyl group” means amonovalent group of the “5-membered aromatic heterocycle” or “6-memberedaromatic heterocycle”.

In the present compound of Formula (1), preferable embodiments of R¹,R², R³, R⁴, R⁵, R⁶, R^(a), R^(b), R^(c), R^(d), R^(e), Ring A, and X areshown below, but the scope of the present invention is not intended tobe limited to the preferable embodiments shown below, each of which maybe optionally combined.

Preferably, R¹ and R² are each independently hydrogen atom or C₁₋₄alkyl, wherein the alkyl may be optionally substituted with 1 to 5substituents independently selected from the group consisting offluorine atom and C₁₋₄ alkoxy.

More preferably, R¹ and R² are each independently hydrogen atom, methyl,ethyl, methoxymethyl, or trifluoromethyl, further preferably hydrogenatom or methyl. Particularly preferably, R¹ is methyl, and R² ishydrogen atom.

Preferably, R³ and R⁴ are each independently hydrogen atom, halogenatom, C₁₋₄ alkyl, or C₁₋₄ alkoxy, wherein the alkyl and the alkoxy maybe optionally substituted with 1 to 5 fluorine atoms. More preferably,R³ and R⁴ are each independently hydrogen atom, fluorine atom, chlorineatom, methyl, difluoromethyl, trifluoromethyl, methoxy, difluoromethoxy,or trifluoromethoxy, further preferably hydrogen atom, fluorine atom,chlorine atom, difluoromethyl, trifluoromethyl, or difluoromethoxy.

Preferably, R⁵ and R⁶ are each independently hydrogen atom, halogenatom, C₁₋₄ alkyl, C₁₋₄ alkoxy, wherein the alkyl and the alkoxy may beoptionally substituted with 1 to 5 fluorine atoms, or —NR^(a)R^(b). Morepreferably, R⁵ and R⁶ are each independently hydrogen atom, fluorineatom, chlorine atom, methyl, ethyl, propyl, methoxy, or —NR^(a)R^(b),further preferably hydrogen atom, fluorine atom, methyl, ethyl, or—NR^(a)R^(b). Still further preferably, they are hydrogen atom, fluorineatom, methyl, or —NH₂. Particularly preferably, they are hydrogen atomor —NH₂.

Preferably, R^(a) and R^(b) are each independently hydrogen atom or C₁₋₄alkyl, wherein the alkyl may be optionally substituted with 1 to 5fluorine atoms. More preferably, R^(a) and R^(b) are each independentlyhydrogen atom or methyl. Further preferably, both are hydrogen atom.

Preferably, R^(c) includes C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy, more preferably methyl or ethyl, further preferably methyl.

Preferably, R^(d) includes hydrogen atom and C₁₋₄ alkyl, more preferablyhydrogen atom or methyl.

Preferably, R^(e) includes hydrogen atom, C₁₋₄ alkyl, and halogen atom,more preferably hydrogen atom or fluorine atom, further preferablyhydrogen atom.

Preferably, X includes nitrogen atom and —CH—, further preferably —CH—.

Preferably, Ring A includes benzene, pyridine, thiophene,1,3-benzodioxole, benzothiophene, benzofuran, and quinoline, morepreferably benzene, thiophene, pyridine, or 1,3-benzodioxole, furtherpreferably benzene or pyridine, particularly preferably benzene.

One embodiment of the compound of Formula (1) includes the following(A).

(A)

A compound of Formula (1), or a pharmaceutically acceptable saltthereof,

wherein R¹ and R² are each independently hydrogen atom or methyl;

R³ and R⁴ are each independently hydrogen atom, fluorine atom, chlorineatom, C₁₋₄ alkyl, or C₁₋₄ alkoxy, wherein the alkyl and the alkoxy maybe optionally substituted with 1 to 5 fluorine atoms;

R⁵ and R⁶ are each independently hydrogen atom, fluorine atom, chlorineatom, methyl, ethyl, propyl, methoxy, or —NR^(a)R^(b);

R^(a) and R^(b) are each independently hydrogen atom, or C₁₋₄ alkyl;

R^(e) is hydrogen atom or fluorine atom;

X is nitrogen atom or —CR^(e)—; and

Ring A is benzene, thiophene, or pyridine.

Another embodiment of the compound of Formula (1) includes the following(B).

(B)

A compound of Formula (1), or a pharmaceutically acceptable saltthereof,

wherein R¹ is methyl;

R² is hydrogen atom;

R³ and R⁴ are each independently hydrogen atom, fluorine atom, chlorineatom, methyl, difluoromethyl, trifluoromethyl, methoxy, difluoromethoxy,or trifluoromethoxy;

R⁵ and R⁶ are each independently hydrogen atom, fluorine atom, methyl,or NH₂;

X is —CH—; and

Ring A is benzene or pyridine.

Among the present compounds, more preferable ones are those which showno or only slightly mechanism-based inhibition (MBI) against CytochromeP450 3A4 (CYP3A4), and which have lower risks for significant sideeffects such as hepatotoxicity as well as drug-drug interactions.

The term “pharmaceutically acceptable salt” includes acid additionsalts, base addition salts, and amino acid salts. For example, the acidaddition salts include inorganic acid salts such as hydrochloride,hydrobromide, sulfate, hydroiodide, nitrate, and phosphate and organicacid salts such as citrate, oxalate, phthalate, fumarate, maleate,succinate, malate, acetate, formate, propionate, benzoate,trifluoroacetate, methanesulfonate, benzenesulfonate,para-toluenesulfonate, and camphorsulfonate. The base addition saltsinclude inorganic base salts such as sodium salt, potassium salt,calcium salt, magnesium salt, barium salt, and aluminum salt and organicbase salts such as trimethylamine, triethylamine, pyridine, picoline,2,6-lutidine, ethanolamine, diethanolamine, triethanolamine,tromethamine, tris(hydroxymethyl)methylamine, tert-butylamine,cyclohexylamine, dicyclohexylamine, and N,N-dibenzylmethylamine. Theamino acid salts include amino acid salts with basic amino acids oracidic amino acids such as arginine, lysine, ornithine, asparagine acid,and glutamic acid. More preferable ones include hydrochloride andphosphate, further preferably a 2.5 phosphate salt.

Preferable salts of starting materials and intermediates and saltsacceptable for pharmaceutical materials are commonly-used non-toxicsalts. Such salts include acid addition salts such as organic acid salts(e.g., acetate, trifluoroacetate, maleate, fumarate, citrate, tartrate,methanesulfonate, benzenesulfonate, formate, and para-toluenesulfonate)and inorganic acid salts (e.g., hydrochloride, hydrobromide,hydroiodide, sulfate, nitrate, and phosphate), salts with amino acids(e.g., arginine, asparagine acid, and glutamic acid), metal salts suchas alkali metal salts (e.g., sodium salt and potassium salt) andalkaline-earth metal salts (e.g., calcium salt and magnesium salt),ammonium salts, organic base salts (e.g., trimethylamine salt,triethylamine salt, pyridine salt, picoline salt, dicyclohexylaminesalt, and N,N′-dibenzylethylenediamine salt), and those which a personskilled in the art can optionally select.

When a salt of the present compound is to be obtained, a salt of thepresent compound may be purified directly in the case where the presentcompound is obtained in the form of such a salt, whereas in the casewhere the present compound is obtained in its free form, such a freeform may be solved or suspended in an appropriate organic solvent,followed by addition of an acid or base, resulting in the formation of acorresponding salt according to common methods.

The present invention includes a compound of Formula (1), or apharmaceutically acceptable salt thereof, or a cocrystal. Such acocrystal includes, for example, a cocrystal (molar ratio of 1:1 to 2.5)of a compound of Formula (1), or a pharmaceutically acceptable saltthereof, with a hydrochloric-acid or phosphoric-acid molecule. Thepresent compound may also exist in the form of a hydrate and/or solvateswith various solvents (e.g., ethanolate), and includes these hydrateand/or solvates as well.

The present compound includes those which may have optical isomers basedon a chiral center, atropisomers based on axial or planar chiralitycaused by hindrance of intramolecular rotation, or other isomers such asstereoisomers, tautomers, and geometric isomers, and all possibleisomers, including these isomers, and a mixture thereof are encompassedwithin the scope of the present invention. In addition to the aboveisomers, any crystalline forms and a mixture thereof are alsoencompassed in the present invention.

In particular, optical isomers and atropisomers may be obtained in amixture having a different steric structure such as a racemic mixture orin an optically active substance in the case where optically activestarting materials or intermediates are used. Racemates of correspondingstarting materials, intermediates, or final products may be physicallyor chemically separated into their optical enantiomers by knownseparation procedures, such as a method with an optically active columnand fractionated crystallization, at an appropriate step of thepreparation process as below, if necessary. For example, in thediastereomer method, two diastereomers are formed from a racemate in areaction with an optically resolving reagent. Each diastereomergenerally has different physical properties, and may be separated byknown procedures such as fractionated crystallization.

The present compound encompasses a prodrug of a compound of Formula (1),or a pharmaceutically acceptable salt thereof, as well as the aboveisomers. The present compound also encompasses compounds where a part orall of atoms constituting a compound of Formula (1) are replaced withisotopes, for example, those which hydrogen is deuterated or tritiated(²H, ³H) and those which ¹²C is replaced with ¹⁴C.

The term “prodrug of a compound of Formula (1)” herein means a compoundthat is converted into a compound of Formula (1) in the reaction withenzymes or gastric acid under physiological conditions in vivo, i.e., acompound that is enzymatically oxidized, reduced, or hydrolyzed tochange into a compound of Formula (1), or a compound that is hydrolyzeddepending on pH changes with gastric acid to change into a compound ofFormula (1).

Preparation of the Present Compound

Preparation of the present compound is illustrated by examplehereinafter, but the present invention is not intended to be limitedthereto.

The present compound can be prepared by, for example, the methods shownin the following Preparation 1 to 12. These Preparation may beoptionally modified on the basis of knowledge of a person skilled inorganic synthetic chemistry. Compounds used for starting materials maybe substituted with their salts or those which a functional group isprotected, if necessary.

In the Preparation as below, when any of functional groups other than areaction site may change depending on reaction conditions or may not besuitable for treatment after reactions, in addition to the case wherethe use of a protecting group is explicitly mentioned, any groups otherthan the reaction site may be protected, if necessary, followed bydeprotection after the completion of reaction or a series of reactions,to give a desired product. Such a protecting group includes any commonprotecting groups described in literature (such as T. W. Greene and P.G. M. Wuts, “Protective Groups in Organic Synthesis”, 3rd Ed., JohnWiley and Sons, Inc., New York (1999)), and the introduction and removalof such a protecting group may be carried out by or in accordance withmethods commonly used in the organic synthetic chemistry (e.g., themethods described in the above literature). Specifically, protectinggroups for amino include, for example, benzyloxycarbonyl,tert-butoxycarbonyl, acetyl, and benzyl and those for hydroxy include,for example, trialkylsilyl, acetyl, and benzyl.

Any starting materials and intermediates used in each of the followingPreparation are commercially available or can be obtained andsynthesized from commercially available compounds or known compounds byor in accordance with methods known by a person skilled in the art. Suchstarting materials and intermediates may be used in their salt forms orin those which any of functional groups are protected, if necessary.

Any of intermediates and desired compounds in the preparation as belowmay be converted into any of other compounds encompassed in the presentinvention by optionally transforming any functional groups thereof orextending various side chains, specifically via amino, hydroxy,carbonyl, or halogen, followed by the above-mentioned protection anddeprotection, if necessary. The transformation of functional groups andextension of side chains may be carried out by or in accordance withgeneral methods commonly used (e.g., R. C. Larock, “ComprehensiveOrganic Transformations”, 2nd Ed., John Wiley and Sons Inc., New York(1999)).

The inert solvent used in the Preparation as below means any of solventsthat do not react with starting materials, reagents, bases, acids,catalysts, and ligands used in reactions.

Preparation 1

Compound (3) is prepared by, for example, the following process.

(In the scheme, R⁷ is methyl or ethyl.)

step 1: Compound (2) may be esterified in a similar manner to knownmethods (e.g., R. C. Larock, “Comprehensive Organic Transformations”,2nd Ed., John Wiley and Sons inc., New York (1999)) to give Compound(3). Compound (2) may be commercially available or synthesized by knownmethods.

Preparation 2

Compound (6) is prepared by, for example, the following processes.

(In the scheme, R¹ and R² are as defined in Item 1; R⁷ is methyl orethyl; PG is a protecting group (such as tert-butoxycarbonyl group andbenzyloxycarbonyl group); and LG is a leaving group (such as iodineatom, bromine atom, chlorine atom, and substituted sulfonyloxy group(e.g., methanesulfonyloxy group, trifluoromethanesulfonyloxy group, andp-toluenesulfonyloxy group)).)

step 2: Compound (6) may be prepared by Mitsunobu reaction of Compound(3) and Compound (4) in an appropriate inert solvent with conventionalmethods. Specifically, the reaction may be carried out in the presenceof triphenylphosphine or tributylphosphine and a Mitsunobu reactionreagent such as diethyl azodicarboxylate, diisopropyl azodicarboxylate,and N,N,N′,N′-tetramethylazodicarboxamide, or with acyanomethylenephosphorane reagent. The reaction temperature of thepresent step generally ranges from −20° C. to a boiling point of thesolvent used herein. The reaction time of the present step ranges from 1minute to 5 days. Compounds (3) and (4) may be commercially available orsynthesized by known methods.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; aromatic hydrocarbons such as benzene and toluene;ether solvents such as tetrahydrofuran, diethyl ether, and 1,4-dioxane;and a mixed solvent thereof.

step 3: Compound (6) may also be prepared by reacting Compound (3) andCompound (5) in the presence of an appropriate base in an appropriateinert solvent according to conventional methods. The reaction may becarried out in the presence of an appropriate phase-transfer catalyst,if necessary. The reaction temperature of the present step generallyranges from −20° C. to a boiling point of the solvent used herein. Thereaction time of the present step ranges from 1 minute to 5 days.Compounds (3) and (5) may be commercially available or synthesized byknown methods.

Examples of the base used in the present step include, for example,organic bases such as triethylamine, N,N-diisopropylethylamine, andpyridine; inorganic bases such as potassium carbonate, sodium carbonate,cesium carbonate, potassium hydrogen carbonate, sodium hydrogencarbonate, potassium dihydrogen phosphate, dipotassium hydrogenphosphate, potassium phosphate, sodium dihydrogen phosphate, disodiumhydrogen phosphate, sodium phosphate, potassium hydroxide, sodiumhydroxide, and sodium hydride; and metal alkoxides such as sodiummethoxide and potassium tert-butoxide.

Examples of the phase-transfer catalyst used in the present stepinclude, for example, tetrabutylammonium hydrogen sulfate.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; ketones such as acetone and methyl ketone; aromatichydrocarbons such as benzene and toluene; ether solvents such astetrahydrofuran, diethyl ether, 1,4-dioxane, and 1,2-dimethoxyethane;lower alcohols such as methanol, ethanol, and 2-propanol; aprotic polarsolvents such as acetonitrile, N,N-dimethylformamide, andN-methyl-2-pyrrolidone; water; and a mixed solvent thereof.

Preparation 3

Compound (9) is prepared by, for example, the following processes.

(In the scheme, Ring A, R¹, R², R³, and R⁴ are as defined in Item 1; R⁷is methyl or ethyl; PG is a protecting group such as tert-butoxycarbonylgroup and benzyloxycarbonyl group; and X¹ is iodine, bromine, orchlorine.)step 4: Compound (7) may be prepared by removing a protecting group ofamine, PG, from Compound (6) in an appropriate inert solvent by any ofvarious methods known to a person skilled in the art (see T. W. Greeneand P. G. M. Wuts, “Protective Groups in Organic Synthesis”, 3rd Ed.,John Wiley and Sons, inc., New York (1999)), followed by cyclization inthe presence of an appropriate base or acid. In the present step, theremoval of a protecting group and cyclization may also be carried outsimultaneously in a single reaction system in the presence of anappropriate base or acid in an appropriate inert solvent according toconventional methods. The reaction temperature of the present stepgenerally ranges from −20° C. to a boiling point of the solvent usedherein. The reaction time of the present step ranges from 1 minute to 5days.

Examples of the base used in the present step include, for example,organic bases such as triethylamine and pyridine; inorganic bases suchas potassium carbonate and sodium carbonate; and metal alkoxides such aspotassium tert-butoxide.

Examples of the acid used in the present step include, for example,inorganic acids such as hydrochloric acid and sulfuric acid and organicacids such as acetic acid and trifluoroacetic acid.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; aromatic hydrocarbons such as benzene and toluene;ether solvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and1,2-dimethoxyethane; lower alcohols such as methanol, ethanol, and2-propanol; aprotic polar solvents such as acetonitrile,N,N-dimethylformamide, and N-methyl-2-pyrrolidone; organic acids such asacetic acid; and a mixed solvent thereof.

step 5: Compound (9) may be prepared in a coupling reaction of Compound(7) and Compound (8) in the presence of an appropriate transition metalcatalyst and base in an appropriate inert solvent according toconventional methods. The reaction may be carried out in the presence ofan appropriate ligand, if necessary. The reaction temperature of thepresent step generally ranges from room temperature to a boiling pointof the solvent used herein. The reaction time of the present step rangesfrom 1 minute to 5 days. Compound (8) may be commercially available orsynthesized by known methods.

Examples of the transition metal catalyst used in the present stepinclude, for example, palladium (II) acetate,tris(dibenzylideneacetone)dipalladium (0),bis(tri-tert-butylphosphine)palladium (0), copper (I) iodide, and copper(II) oxide.

Examples of the ligand used in the present step include, for example,tri-tert-butylphosphine,2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl,4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, andN,N′-dimethylethylenediamine.

Examples of the base used in the present step include, for example,metal alkoxides such as sodium tert-butoxide and inorganic bases such astripotassium phosphate and potassium carbonate.

Examples of the inert solvent used in the present step include, forexample, aromatic hydrocarbons such as benzene and toluene; ethersolvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and1,2-dimethoxyethane; aprotic polar solvents such asN,N-dimethylformamide and N,N-dimethylacetamide; and a mixed solventthereof.

Preparation 4

Compound (9) is also prepared by, for example, the following processes.

(In the scheme, Ring A, R¹, R², R³, and R⁴ are as defined in Item 1; andR⁷ and X¹ are as defined above.)step 6: Compound (13) may be prepared by reacting Compound (10) andCompound (11) in an appropriate inert solvent according to conventionalmethods. The reaction may be carried out in the presence of a base oracid with an appropriate additive, if needed, and in the presence of anappropriate phase-transfer catalyst. The reaction temperature of thepresent step generally ranges from −20° C. to a boiling point of thesolvent used herein. The reaction time of the present step ranges from 1minute to 10 days. Compounds (10) and (11) may be commercially availableor synthesized by known methods.

Examples of the additive used in the present step include, for example,lithium bromide.

Examples of the base used in the present step include, for example,organic bases such as triethylamine and pyridine; and inorganic basessuch as potassium carbonate, sodium carbonate, potassium hydroxide, andsodium hydroxide.

Examples of the acid used in the present step include, for example,inorganic acids such as hydrochloric acid and sulfuric acid and organicacids such as p-toluenesulfonic acid and trifluoroacetic acid.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; aromatic hydrocarbons such as benzene and toluene;ether solvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and1,2-dimethoxyethane; lower alcohols such as methanol, ethanol, and2-propanol; aprotic polar solvents such as acetonitrile,N,N-dimethylformamide, and N-methyl-2-pyrrolidone; and a mixed solventthereof.

step 7: Compound (13) may also be prepared by coupling Compound (8) andCompound (12) in the presence of an appropriate transition metalcatalyst and base in an appropriate inert solvent or under solvent-freecondition.

The reaction temperature of the present step generally ranges from −20°C. to a boiling point of the solvent used herein. The reaction time ofthe present step ranges from 1 minute to 5 days. Compound (8) andCompound (12) may be commercially available or synthesized by knownmethods.

Examples of the transition metal catalyst used in the present stepinclude, for example, palladium (II) acetate,tris(dibenzylideneacetone)dipalladium (0),bis(tri-tert-butylphosphine)palladium (0), copper (I) chloride, copper(I) bromide, copper (I) iodide, copper (I) acetate, and copper (II)oxide.

Examples of the base used in the present step include, for example,organic bases such as triethylamine and pyridine; and inorganic basessuch as potassium carbonate, sodium carbonate, cesium carbonate,potassium hydroxide, and sodium hydroxide.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; aromatic hydrocarbons such as benzene and toluene;ether solvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and1,2-dimethoxyethane; lower alcohols such as methanol, ethanol, and2-propanol; aprotic polar solvents such as acetonitrile,N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethylsulfoxide;water; and a mixed solvent thereof.

step 8: Compound (14) may be prepared by Mitsunobu reaction of Compound(3) and Compound (13) in an appropriate inert solvent according toconventional methods. Specifically, the reaction may be carried out inthe presence of triphenylphosphine or tributylphosphine and a Mitsunobureaction reagent such as diethyl azodicarboxylate, diisopropylazodicarboxylate, and N,N,N′,N′-tetramethylazodicarboxamide, or with acyanomethylenephosphorane reagent. The reaction temperature of thepresent step generally ranges from −20° C. to a boiling point of thesolvent used herein. The reaction time of the present step ranges from 1minute to 5 days. Compound (3) may be commercially available orsynthesized by known methods.

Examples of the inert solvent used in the present step include, forexample, aromatic hydrocarbons such as benzene and toluene; ethersolvents such as tetrahydrofuran, diethyl ether, and 1,4-dioxane; and amixed solvent thereof.

step 9: Compound (9) may be prepared by cyclization of Compound (14) inthe presence of an appropriate base or acid in an appropriate inertsolvent according to conventional methods. The reaction temperature ofthe present step generally ranges from −20° C. to a boiling point of thesolvent used herein. The reaction time of the present step ranges from 1minute to 5 days.

Examples of the base used in the present step include, for example,organic bases such as triethylamine and pyridine; inorganic bases suchas potassium carbonate and sodium carbonate; and metal alkoxides such aspotassium tert-butoxide.

Examples of the acid used in the present step include, for example,inorganic acids such as hydrochloric acid and sulfuric acid and organicacids such as p-toluenesulfonic acid monohydrate, acetic acid, andtrifluoroacetic acid.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform anddichloromethane; aromatic hydrocarbons such as benzene and toluene;ether solvents such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and1,2-dimethoxyethane; lower alcohols such as methanol, ethanol, and2-propanol; aprotic polar solvents such as acetonitrile,N,N-dimethylformamide, and N-methyl-2-pyrrolidone; and a mixed solventthereof.

Preparation 5

Compound (15) is prepared by, for example, the following process.

(In the scheme, Ring A, R¹, R², R³, and R⁴ are as defined in Item 1; andX¹ is as defined above.)step 10: Compound (15) may be prepared by reacting Compound (9) and anappropriate halogenating agent in an appropriate inert solvent accordingto conventional methods. The reaction may be carried out in the presenceof an appropriate additive or acid, if necessary. The reactiontemperature of the present step generally ranges from −20° C. to aboiling point of the solvent used herein. The reaction time of thepresent step ranges from 1 minute to 5 days.

Examples of the halogenating agent used in the present step include, forexample, N-iodosuccinimide, N-bromosuccinimide, N-chlorosuccinimide,iodine, iodine monochloride, bromine, and1,3-diiodo-5,5-dimethylhydantoin.

Examples of the additive used in the present step include, for example,ammonium cerium (IV) nitrate, sodium acetate, and iron.

Examples of the acid used in the present step include, for example,hydrochloric acid, sulfuric acid, acetic acid, para-toluenesulfonicacid, and pyridinium para-toluenesulfonate.

Examples of the inert solvent used in the present step include, forexample, halogenated hydrocarbons such as chloroform, dichloromethane,and carbon tetrachloride; aprotic polar solvents such asN,N-dimethylformamide and ethyl acetate; protic polar solvents such asacetic acid; and a mixed solvent thereof.

Preparation 6

Compound (1) is prepared by, for example, the following

(In the scheme, Ring A, X, R¹, R², R³, R⁴, R⁵, and R⁶ are as defined inItem 1; X¹ is as defined above; and R^(A) is boronic acid or boronicacid ester.)step 11: Compound (1) may be prepared in a coupling reaction of Compound(15) and Compound (16) in the presence of an appropriate transitionmetal catalyst and base in an appropriate inert solvent according toconventional methods. The present step may also be carried out in thepresence of an appropriate ligand, if necessary. The reactiontemperature of the present step generally ranges from room temperatureto a boiling point of the solvent used herein, preferably from 50° C. to150° C. The reaction time of the present step generally ranges from 1minute to 5 days, preferably from 1 minute to 2 days. The present stepmay also be carried out under microwave irradiation. Compound (16) maybe commercially available or synthesized by known methods.

Examples of the transition metal catalyst used in the present stepinclude, for example, tetrakis(triphenylphosphine)palladium (0),palladium (II) acetate, palladium (II) chloride,tris(dibenzylideneacetone)dipalladium (0),dichlorobis(triphenylphosphine)palladium (II),dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium (II)dichloromethane adduct, anddichlorobis[di-tert-butyl(4-dimethylaminophenyl)phosphino]palladium(II).

Examples of the base used in the present step include, for example,sodium carbonate, potassium carbonate, cesium carbonate, sodiumhydroxide, potassium hydroxide, and potassium phosphate.

Examples of the ligand used in the present step include, for example,triphenylphosphine, tri-tert-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, and2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl.

Examples of the inert solvent used in the present step include, forexample, ether solvents such as tetrahydrofuran, diethyl ether,1,4-dioxane, and 1,2-dimethoxyethane; aprotic polar solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,and acetonitrile; aromatic hydrocarbons such as benzene and toluene;water; and a mixed solvent thereof.

Preparation 7

Compound (1) is also prepared by, for example, the following processes.

(In the scheme, Ring A, X, R¹, R², R³, R⁴, R⁵, and R⁶ are as defined inItem 1; and X¹ and R^(A) are as defined above.)step 12: Compound (17) may be prepared in a similar manner to step 10with Compound (7).step 13: Compound (18) may be prepared in a similar manner to step 11with Compound (17) and Compound (16).step 14: Compound (1) may be prepared in a similar manner to step 5 withCompound (8) and Compound (18).

Preparation 8

Compound (1) is also prepared by, for example, the following processes.

(In the scheme, Ring A, X, R¹, R², R³, R⁴, R⁵, and R⁶ are as defined inItem 1; X¹ and R^(A) are as defined above; and R⁸ is C₁₋₄ alkyl.)

step 15: Compound (20) may be prepared by reacting Compound (15) andCompound (19) in the presence of an appropriate base in an appropriateinert solvent according to conventional methods. The reactiontemperature of the present step generally ranges from −78° C. to aboiling point of the solvent used herein, preferably from −78° C. toroom temperature. The reaction time of the present step generally rangesfrom 1 minute to 5 days, preferably from 1 minute to 2 days. Compound(19) may be commercially available or synthesized by known methods.

Examples of the base used in the present step include, for example,isopropylmagnesium chloride-lithium chloride complex, n-butyllithium,sec-butyllithium, tert-butyllithium, lithium diisopropylamide, lithiumtetramethylpiperidide, lithium hexamethyldisilazide, sodiumhexamethyldisilazide, and potassium hexamethyldisilazide.

Examples of the inert solvent used in the present step include, forexample, ether solvents such as tetrahydrofuran, diethyl ether,1,4-dioxane, and 1,2-dimethoxyethane; saturated hydrocarbons such asn-hexane, n-heptane, and cyclohexane; and a mixed solvent thereof.

step 16: Compound (1) may be prepared in a similar manner to step 11with Compound (20) and Compound (21). Compound (21) may be commerciallyavailable or synthesized by known methods.

Preparation 9

Compound (15) is also prepared by, for example, the following processes.

(In the scheme, Ring A, R¹, R², R³, and R⁴ are as defined in Item 1; andR⁷ and X¹ are as defined above.)step 17: Compound (23) may be prepared in a similar manner to step 8with Compound (13) and Compound (22). Compound (22) may be commerciallyavailable or synthesized by known methods.step 18: Compound (15) may be prepared in a similar manner to step 9with Compound (23).

Preparation 10

Compound (15) is also prepared by, for example, the following processes.

(In the scheme, Ring A, R¹, R², R³, and R⁴ are as defined in Item 1; andR⁷ and X¹ are as defined above.)

step 19: Compound (24) may be prepared by hydrolysis of the ester groupof Compound (23) in an appropriate inert solvent by any of variousmethods known to a person skilled in the art (e.g., methods described inR. C. Larock, “Comprehensive Organic Transformations”, 2nd Ed., JohnWiley and Sons, Inc., New York (1999)) according to conventionalmethods.

step 20: Compound (15) may be prepared in a similar manner to step 9with Compound (24).

Preparation 11

Compound (26) is also prepared by, for example, the following process.

(In the scheme, Ring A, X, R¹, R², R³, R⁴, and R⁶ are as defined in Item1; and X² is fluorine atom, chlorine atom, bromine atom, or iodineatom.)step 21: Compound (26) may be prepared by reacting Compound (25) and ahalogenating agent in an appropriate inert solvent according toconventional methods. The reaction may also be carried out in thepresence of an additive or acid, if necessary. The reaction temperaturegenerally ranges from −20° C. to a boiling point of the solvent usedherein. The reaction time ranges from 1 minute to 5 days.

Examples of the halogenating agent herein include, for example,1-fluoro-4-methyl-1,4-diazoniabicyclo[2,2,2]octanebis(tetrafluoroborate), 1-fluoropyridinium trifluoromethanesulfonate,N-fluorobenzenesulfonimide, N-iodosuccinimide, N-bromosuccinimide,N-chlorosuccinimide, iodine, iodine monochloride, bromine, and1,3-diiodo-5,5-dimethylhydantoin.

Examples of the additive herein include, for example, ammonium cerium(IV) nitrate, sodium acetate, and iron.

Examples of the acid herein include, for example, hydrochloric acid,sulfuric acid, acetic acid, para-toluenesulfonic acid, and pyridiniumpara-toluenesulfonate.

Examples of the inert solvent herein include, for example, halogenatedhydrocarbons such as chloroform, dichloromethane, and carbontetrachloride; aprotic polar solvents such as acetonitrile,N,N-dimethylformamide, and ethyl acetate; protic polar solvents such asacetic acid; and a mixed solvent thereof.

Preparation 12

Compound (1) is also prepared by, for example, the following processes.

(In the scheme, Ring A, X, R¹, R², R³, R⁴, R⁵, and R⁶ are as defined inItem 1; X² is as defined above; and R⁹ is vinyl or allyl.)step 22: Compound (1) may be prepared by coupling Compound (26) and aboronic acid reagent or alkylzinc reagent in the presence of anappropriate transition metal catalyst in an appropriate inert solvent.The present step may also be carried out in the presence of anappropriate base and/or an appropriate ligand, if necessary. Thereaction temperature of the present step generally ranges from roomtemperature to a boiling point of the solvent used herein, preferablyfrom 50° C. to 150° C. The reaction time of the present step generallyranges from 1 minute to 5 days, preferably from 1 minute to 2 days. Thepresent step may also be carried out under microwave irradiation.

Examples of the boronic acid used in the present step include, forexample, methylboronic acid, ethylboronic acid, and trimethylboroxine;but are not limited thereto.

Examples of the alkylzinc reagent used in the present step include, forexample, methylzinc chloride and ethylzinc chloride; but are not limitedthereto.

Examples of the transition metal catalyst used in the present stepinclude, for example, tetrakis(triphenylphosphine)palladium (0),palladium (II) acetate, palladium (II) chloride,tris(dibenzylideneacetone)dipalladium (0),dichlorobis(triphenylphosphine)palladium (II),dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium (II)dichloromethane adduct,dichlorobis[di-tert-butyl(4-dimethylaminophenyl)phosphino]palladium(II), and bis-(tri-tert-butylphosphine)palladium (0); but are notlimited thereto.

Examples of the base used in the present step include, for example,sodium carbonate, potassium carbonate, cesium carbonate, sodiumhydroxide, potassium hydroxide, and potassium phosphate; but are notlimited thereto.

Examples of the ligand used in the present step include, for example,triphenylphosphine, tri-tert-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, and2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; but are notlimited thereto.

Examples of the inert solvent used in the present step include, forexample, ether solvents such as tetrahydrofuran, diethyl ether,1,4-dioxane, and 1,2-dimethoxyethane; aprotic polar solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,and acetonitrile; aromatic hydrocarbons such as benzene and toluene;water; and a mixed solvent thereof; but are not limited thereto.

step 23: Compound (27) may be prepared in a coupling reaction ofCompound (26) and a boronic acid reagent in the presence of anappropriate transition metal catalyst and an appropriate base in anappropriate inert solvent according to conventional methods. The presentstep may also be carried out in the presence of an appropriate ligand,if necessary. The reaction temperature of the present step generallyranges from room temperature to a boiling point of the solvent usedherein, preferably from 50° C. to 150° C. The reaction time of thepresent step generally ranges from 1 minute to 5 days, preferably from 1minute to 2 days. The present step may also be carried out undermicrowave irradiation.

Examples of the boronic acid used in the present step include, forexample, 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane,cis-propenylboronic acid, trans-propenylboronic acid, and allylboronicacid pinacol ester; but are not limited thereto.

Examples of the transition metal catalyst used in the present stepinclude, for example, tetrakis(triphenylphosphine)palladium (0),palladium (II) acetate, palladium (II) chloride,tris(dibenzylideneacetone)dipalladium (0),dichlorobis(triphenylphosphine)palladium (II),dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium (II)dichloromethane adduct, anddichlorobis[di-tert-butyl(4-dimethylaminophenyl)phosphino]palladium(II); but are not limited thereto.

Examples of the base used in the present step include, for example,sodium carbonate, potassium carbonate, cesium carbonate, sodiumhydroxide, potassium hydroxide, and potassium phosphate; but are notlimited thereto.

Examples of the ligand used in the present step include, for example,triphenylphosphine, tri-tert-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, and2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; but are notlimited thereto.

Examples of the inert solvent used in the present step include, forexample, ether solvents such as tetrahydrofuran, diethyl ether,1,4-dioxane, and 1,2-dimethoxyethane; aprotic polar solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,and acetonitrile; aromatic hydrocarbons such as benzene and toluene;water; and a mixed solvent thereof; but are not limited thereto.

step 24: Compound (1) may be prepared by hydrogenation of an unsaturatedcarbon bond of Compound (27) in an appropriate inert solvent by any ofvarious methods known to a person skilled in the art (e.g., methodsdescribed in R. C. Larock, “Comprehensive Organic Transformations”, 2ndEd., John Wiley and Sons, Inc., New York (1999)) according toconventional methods. The reaction temperature of the present stepgenerally ranges from room temperature to a boiling point of the solventused herein. The reaction time of the present step ranges from 1 minuteto 5 days.

Bases used in each step of each Preparation should be selectedappropriately depending on reactions and starting materials, andinclude, for example, alkali bicarbonates such as sodium bicarbonate andpotassium bicarbonate; alkali carbonates such as sodium carbonate andpotassium carbonate; metal hydrides such as sodium hydride and potassiumhydride; alkali metal hydroxides such as sodium hydroxide and potassiumhydroxide; alkali metal alkoxides such as sodium methoxide and sodiumtert-butoxide; organic metal bases such as butyllithium and lithiumdiisopropylamide; and organic bases such as triethylamine,diisopropylethylamine, pyridine, 4-dimethylaminopyridine (DMAP), and1,8-diazabicyclo[5.4.0]-7-undecene (DBU).

Solvents used in each step of each Preparation should be selectedappropriately depending on reactions and starting materials, andinclude, for example, alcohols such as methanol, ethanol, andisopropanol; ketones such as acetone and methyl ketone; halogenatedhydrocarbons such as methylene chloride and chloroform; ethers such astetrahydrofuran (THF) and 1,4-dioxane; aromatic hydrocarbons such astoluene and benzene; aliphatic hydrocarbons such as hexane and heptane;esters such as ethyl acetate and propyl acetate; amides such asN,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone; sulfoxides suchas dimethylsulfoxide (DMSO); and nitriles such as acetonitrile; andthese solvents may be used in a single component or in a mixture of anytwo or more solvents. An organic base may be used in place of a solventdepending on reactions.

Intermediates and desired compounds in each Preparation may be isolatedwith purification procedures commonly used in the organic syntheticchemistry, such as neutralization, filtration, extraction, washing,drying, concentration, recrystallization, and a variety ofchromatography (e.g., silica gel column chromatography, ion-exchangecolumn chromatography, and preparative liquid chromatography).

Solvents for recrystallization include, for example, alcohol solventssuch as methanol, ethanol, and 2-propanol; ether solvents such asdiethyl ether; ester solvents such as ethyl acetate; aromatichydrocarbon solvents such as benzene and toluene; ketone solvents suchas acetone; halogen solvents such as dichloromethane and chloroform;hydrocarbon solvents such as hexane; aprotic solvents such asN,N-dimethylformamide and acetonitrile; water; and a mixed solventthereof. Other purification procedures include methods described inExperimental Chemistry (edited by The Chemical Society of Japan,Maruzen) vol. 1. Molecular structures of the present compound canreadily be determined by spectroscopy such as the nuclear magneticresonance method, infrared absorption technique, and circular dichroicspectroscopy and mass spectroscopy with reference to correspondingstructures derived from starting materials. Intermediates may also beused in a next reaction without any specific purification.

The present compound may cause asymmetry or have a substituent with anasymmetric carbon, and such a compound may have optical isomers. Thepresent compound includes a mixture of these isomers and a separatedisomer, and may be prepared according to conventional methods. Suchmethods include, for example, those using a starting material with anasymmetric center and those which asymmetry is introduced during any ofintermediate steps. For example, an optical isomer may be obtained bystarting from a corresponding optically active starting material or byoptical resolution in any of appropriate steps during its preparationprocess.

Such optical resolution includes, for example, HPLC with a separationcolumn for optical isomers. When a compound of Formula (1) orintermediates thereof may have a basic functional group, diastereomertechnique may be used to form a corresponding salt with an opticallyactive acid (e.g., monocarboxylic acid such as mandelic acid,N-benzyloxyalanine, and lactic acid; dicarboxylic acid such as tartaricacid, o-diisopropylidenetartaric acid, and malic acid; and sulfonic acidsuch as camphorsulfonic acid and bromocamphorsulfonic acid) in an inertsolvent (e.g., alcohol solvents such as methanol, ethanol, and2-propanol; ether solvents such as diethyl ether; ester solvents such asethyl acetate; hydrocarbon solvents such as toluene; aprotic solventssuch as acetonitrile; and a mixed solvent of any two or more selectedfrom the above-mentioned solvents). When the present compound orintermediates thereof may have an acidic functional group such ascarboxyl group, optical resolution may be carried out to form acorresponding salt with an optically active amine (e.g., organic aminessuch as 1-phenylethylamine, quinine, quinidine, cinchonidine,cinchonine, and strychnine).

The temperature forming a salt is selected from the range from −50° C.to a boiling point of a solvent, preferably the range from 0° C. to aboiling point, more preferably the range from room temperature to aboiling point of a solvent. In order to improve the optical purity, itis desirable to increase the temperature to around a boiling point of asolvent. A salt precipitated may be optionally cooled down to becollected by filtration so as to improve yields. The amount of anoptically active acid or amine used ranges from about 0.5 to about 2.0equivalents to a corresponding substrate, preferably around 1equivalent. A crystal may be optionally recrystallized in an inertsolvent (e.g., alcohol solvents such as methanol, ethanol, and2-propanol; ether solvent such as diethyl ether; ester solvents such asethyl acetate; hydrocarbon solvents such as toluene; aprotic solventssuch as acetonitrile; and a mixed solvent of any two or more selectedfrom the above-mentioned solvents) to give a corresponding highly-pureoptically-active salt. An optically resolved salt may be optionallytreated with an acid or base according to conventional methods to give acorresponding free form.

The present compound has mGlu2 receptor negative allosteric modulator(NAM) activity, and may be a novel therapeutic agent and/or preventiveagent for diseases involving Group II mGlu receptors (i.e., metabotropicglutamate receptor subtype 2 (mGluR2) and/or metabotropic glutamatereceptor subtype 3 (mGluR3), preferably mGluR2), which shows negativeallosteric modulation to Group II mGlu receptors. Such diseasesinvolving Group II mGlu receptors include psychiatric diseases andneurodegenerative diseases, specifically major depressive disorder,depressive disorders (such as major depression, treatment-resistantdepression, and chronic depression), bipolar and related disorders (suchas bipolar depression), anxiety disorders (such as generalized anxietydisorder, panic disorder, social anxiety disorder, and specific phobia),posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, and sleep disorder.

Among these psychiatric diseases and neurodegenerative diseases, apreferable subject disease is major depressive disorder, depressivedisorders (such as major depression, treatment-resistant depression, andchronic depression), bipolar and related disorders (such as bipolardepression), anxiety disorders (such as generalized anxiety disorder,panic disorder, social anxiety disorder, and specific phobia),posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, Alzheimer's disease, cognitive dysfunction, dementia,drug dependence, obesity, seizure, tremor, pain, or sleep disorder.

The administration route of the present compound may be any of oral,parenteral, or intrarectal administration, and the daily dose variesdepending on conditions such as compounds, administration routes, andsymptoms or ages of patients. In the case of oral administration, about0.01 to 1000 mg, preferably about 0.1 to 500 mg, per day may beadministered to an adult in a single dose or in several divided doses.

The present compound may be orally or parenterally administered directlyor in a suitable dosage form after formulation. Such a dosage formincludes, for example, tablets, capsules, powders, granules, liquids,suspensions, injections, patches, and cataplasms; but is not limitedthereto. Formulations are prepared with pharmaceutically acceptableexcipients according to known methods. Such excipients can be selectedfrom vehicles, disintegrants, binders, fluidizers, lubricants, coatingagents, solubilizers, solubilizing agents, thickening agents,dispersants, stabilizing agents, sweetening agents, and fragrancesdepending on the purpose. Such excipients include, for example, lactose,mannitol, crystalline cellulose, low-substituted hydroxypropylcellulose,corn starch, partly pregelatinized starch, carmellose calcium,croscarmellose sodium, hydroxypropylcellulose,hydroxypropylmethylcellulose, polyvinyl alcohol, magnesium stearate,sodium stearyl fumarate, polyethylene glycol, propylene glycol, titaniumoxide, and talc.

The present compound may be used in combination with one or moreantipsychotic drugs to treat one or more psychiatric diseases orneurodegenerative diseases described herein. Such antipsychotic drugsinclude, for example, therapeutic agents of major depressive disorder,depressive disorders (such as major depression, treatment-resistantdepression, and chronic depression), bipolar and related disorders (suchas bipolar depression), anxiety disorders (such as generalized anxietydisorder, panic disorder, social anxiety disorder, and specific phobia),posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, and sleep disorder. The administration intervalof the present compound and these therapeutic agents is not limited;i.e., these may be administered to a subject at the same time or with asuitable interval. Alternatively, the present compound and any of thesetherapeutic agents may be formualted into a single combination drug. Thedose of these therapeutic agents can be suitably determined on the basisof clinically-used doses thereof. The combination ratio of the presentcompound and any of these therapeutic agents can be suitably determinedon the basis of the condition such as subjects to be administered,administration routes, target diseases, symptoms, and combinationsthereof.

When the present compound is used for an active pharmaceuticalingredient, it is not intended to be used only for human, but it can beused for other animals, such as cats, dogs, cows, chickens, and fishes,besides human.

The present invention is explained in more detail as below by referringto Reference examples, Examples, and Tests; however, the technical scopeof the present invention is not limited thereto. The compound names usedin Reference examples and Examples hereinafter are not necessarily basedon IUPAC nomenclature system. In order to simplify descriptions,abbreviations may be used.

EXAMPLES

Compounds were identified by proton nuclear magnetic resonancespectroscopy (¹H-NMR), LC-MS, and the like. For the nuclear magneticresonance spectroscopy, tetramethylsilane was used as an internalstandard.

Silica gel columns and amino columns manufactured by Yamazen Corporationwere used for column chromatography and amino chromatography inReference examples and Examples. In purification by TLC, Silica gel60F254 (Merck) was used for TLC (silica gel plate), and TLC plate NH(Fuji Silysia) was used for TLC (NH silica gel plate).

The following apparatuses were used in Reference examples and Examples.Various data were obtained with the following apparatuses in Referenceexamples and Examples.

Microwave reactor: Biotage AB Initiator

NMR spectra: [¹H-NMR] 400 MHz: JEOL JNM-AL series AL 400

LC-MS spectra: Waters ACQUITY™ UltraPerformance LC High-performanceliquid chromatograph (HPLC): Shimazu LC-20

Powder X-ray diffraction: Spectris Power X-ray diffraction systemEmpyrian

CHN Elemental analyzer: FlasH 2000 manufactured by Thermo FisherScientific Inc.

Ion analyzer: ICS-5000+ manufactured by Thermo Fisher Scientific Inc.

Compounds in Reference examples and Examples were named by ACD/Name(ACD/Labs 12.0, Advanced Chemistry Development Inc.).

LC-MS data in Reference examples and Examples were measured under thefollowing conditions. Observed values in mass spectroscopy [MS(m/z)] areshown in [M+H]⁺.

Measurement Conditions

Column: ACQUITY UPLC BEH C18 1.7 μm 2.1×30 mm column

Solvent: Solution A: 0.05% HCOOH/H₂O, Solution B: CH₃CN

Gradient conditions:

0.0-1.3 min; A/B=90/10 to 5/95 (linear gradient)

1.3-1.5 min; A/B=90/10

Flow rate: 0.80 mL/min

UV: 220 nm, 254 nm

Column temperature: 40° C.

Data of high-performance liquid chromatograph (HPLC) in Referenceexamples and Examples were measured under the following conditions.Retention times are shown in Rt (min)

Column: Phenomenex Kinetex 2.6 μm C18 (75×3.0 mm)

Solvent: Solution A: 0.035% TFA/H₂O, Solution B: 0.035% TFA/CH₃CN

Gradient conditions:

0.0 min; A/B=99/1

0.0-5.70 min; A/B=99/1 to 1/99

-   -   (Linear gradient)

5.70-8.00 min; A/B=1/99

Flow rate: 0.90 mL/min

UV: 220 nm, 254 nm

Column temperature: 40° C.

Powder X-ray diffraction measurement in Reference examples and Exampleswere conducted under the following conditions.

X-ray tube: CuKα (wavelength: 1.54 angstrom)

Tube voltage: 45 kV

Tube current: 40 mA

Measurement range: 4 to 40 degrees (20)

Step range: 0.013 degree

Integration time: 100 seconds/step

Diffraction patterns (XRD spectra) obtained are shown in FIGS. 1 to 3.

Crystalline forms may be determined on the basis of characteristicdiffraction peaks of each crystal shown in the diffraction diagrams ofFIGS. 1 to 3.

Major and characteristic diffraction peaks determined in the diffractionpatterns of FIGS. 1 to 3 are shown as below. Diffraction peak values ofdiffraction angles 2θ (°) in the following Examples may comprise acertain amount of measurement deviations depending on measurementapparatuses or measurement conditions. Specifically, such measurementdeviations may be within the range of ±0.2, preferably ±0.1.

CHN elemental analyses in Reference examples and Examples were conductedunder the following conditions.

Combustion furnace temperature: 1000° C.

Reducing furnace temperature: 700° C.

Temperature in constant temperature bath: 55° C.

Analysis time: 600 seconds

Flow rate of helium gas: 110 mL/min

Injection rate of oxygen gas: 75 mL/min

Ion analyses in Reference examples and Examples were conducted under thefollowing conditions.

Cartridge for pretreatment of samples: TOYO IC-SP M

Detector: Conductivity detector

Guard column: IonPac AG11-HC (0.4 mm i.d.×50 mm, Thermo FisherScientific)

Column: IonPac AS11-HC (0.4 mm i.d.×250 mm, Thermo Fisher Scientific)

Suppressor: ACES-300 (4 mm i.d., Thermo Fisher Scientific)

Column oven: 30° C.

Flow rate: 0.015 mL/min

Injection rate: 0.4 μL

Analysis time: 18 min

Eluent: potassium hydroxide solution prepared with Eluent generator EGCKOH (capillary)

Gradient conditions (eluent concentrations)

0-5 min; 10 mM

5-10 min; 10-30 mM (Linear gradient)

10-18 min; 30 mM

The following abbreviations may be used in Reference examples andExamples.

CDCl₃: deuterochloroformCD₃OD: deuteromethanolDMSO-d₆: deuterodimethylsulfoxides: singletd: doublett: tripletq: quartetm: multipletbr: broaddd: double doublettd: triple doubletJ: coupling constant

Hz: Hertz

min: minuteatm: atmosphereHATU: O-(7-aza-1H-benzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphateHPLC: High-performance liquid chromatographTHF: tetrahydrofuranDME: 1,2-dimethoxyethaneTFA: trifluoroacetic acid

DMF: N,N-dimethylformamide

HBTU: O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphateX-phos: 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenylS-phos: 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl

N.D.: Not Detected RLU: Relative Light Unit Reference Example 1: ethyl1-{(2S)-1-[(tert-butoxycarbonyl)amino]propan-2-yl}-1H-pyrazolo-5-carboxylate

To a solution of tert-butyl N-[(2R)-2-hydroxypropyl]carbamate (18.3 g)in THF (130 mL) were added ethyl 1H-pyrazole-3-carboxylate (16.1 g) andtriphenylphosphine (30.2 g) at room temperature, and then thereto wasadded dropwise diisopropyl azodicarboxylate (60.6 mL, 1.9 mol/L toluenesolution) over 30 minutes. The mixture was stirred further at roomtemperature for 2 hours, and then thereto was added water (130 mL). Themixture was stirred for 30 minutes. The mixture was extracted with ethylacetate twice, and the separated organic layers were combined and driedover anhydrous sodium sulfate, filtered, and concentrated under reducedpressure. To the resulted residue was added hexane:diethyl ether (1:1,200 mL), and the resulted solid was filtered off. The filtrate wasconcentrated under reduced pressure to give a crude product.

The resulted crude product was purified by silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (26.5g).

¹H-NMR (400 MHz, CDCl₃) δ: 7.52 (1H, d, J=1.8 Hz), 6.83 (1H, d, J=1.8Hz), 5.58-5.48 (1H, m), 4.88 (1H, s), 4.34 (2H, q, J=7.1 Hz), 3.66-3.49(2H, m), 1.47-1.33 (15H, m)

Reference Example 2:(7S)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

To a solution of the compound of Reference example 1 (26.5 g) in toluene(90 mL) was added TFA (27.8 mL) at ice bath temperature, and the mixturewas stirred at room temperature overnight. The reaction mixture wasconcentrated under reduced pressure, and the residue was dissolved inDMF (150 mL). Thereto was added dropwise triethylamine (37.9 mL) at roomtemperature. The reaction mixture was heated to reflux for 7 hours, andthen thereto was added water (300 mL). The mixture was stirred foradditional 10 minutes. The mixture was extracted withchloroform:methanol (4:1) 14 times, and then the separated organiclayers were combined and dried under anhydrous sodium sulfate, filtered,and concentrated under reduced pressure. To the resulted residue wasadded diethyl ether (100 mL), and the mixture was stirred. The resultedsolid was collected by filtration (6.51 g). The filtrate wasconcentrated under reduced pressure, and to the resulted residue wasadded diethyl ether (100 mL). The mixture was stirred, and the resultedsolid was collected by filtration (2.51 g). The resulted solids werecombined to give the titled compound (8.66 g).

¹H-NMR (400 MHz, CDCl₃) δ: 7.57 (1H, d, J=2.4 Hz), 6.88 (1H, d, J=2.4Hz), 6.88-6.82 (1H, m), 4.60-4.50 (1H, m), 3.80 (1H, ddd, J=7.6, 4.8,3.6 Hz), 3.49 (1H, ddd, J=10.4, 7.6, 2.8 Hz), 1.62 (3H, d, J=6.1 Hz).

Reference Example 3:(7S)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

To a suspension of 1-bromo-4-(trifluoromethyl)benzene (60.6 g), thecompound of Reference example 2 (33.92 g), and potassium carbonate (62g) in toluene (746 mL) were added N,N′-dimethylethylenediamine (11.87 g)and copper iodide (8.55 g), and the mixture was heated to reflux for 6hours. The reaction solution was let cool to room temperature, and thenthereto were added 14% ammonia water (750 mL) and ethyl acetate (750mL). The mixture was stirred at room temperature for 30 minutes. Themixture was separated into layers, and the organic layer was washedsequentially with 14% ammonia water (750 mL) and brine (400 mL), andthen dried over anhydrous sodium sulfate, filtered, and concentratedunder reduced pressure. To the residue were added isopropanol (760 mL),activated carbon (7.6 g), and silica gel (24 g), and the mixture wasstirred at room temperature for 1 hour. The mixture was filtered throughCelite and washed with ethyl acetate (200 mL) three times, and then thefiltrate was concetrated under reduced pressure to give the titledcompound (71.8 g).

1H-NMR (400 MHz, CDCl₃) δ: 7.68 (2H, d, J=8.5 Hz), 7.60 (1H, d, J=1.8Hz), 7.49 (2H, d, J=8.5 Hz), 6.97 (1H, d, J=1.8 Hz), 4.75-4.67 (1H, m),4.21 (1H, dd, J=12.5, 4.3 Hz), 3.95 (1H, dd, J=12.5, 7.6 Hz), 1.69 (3H,d, J=6.7 Hz).

Reference Example 4:(7S)-3-iodo-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A suspension of the compound of Reference example 3 (104.9 g) and1,3-diiodo-5,5-dimethylhydantoin (88 g) in acetic acid (662 mL) wasstirred at 100° C. for 1 hour. The reaction suspension was let cool toroom temperature, and then thereto was added dropwise water (330 mL).The mixture was stirred for 30 minutes. To the reaction mixture wereadded dropwise hexane (200 mL) and water (990 mL), and the mixture wasstirred for 30 minutes. The resulted solid was collected by filtrationand washed with hexane (150 mL) three times to give a crude product (146g). To the resulted crude product was added isopropanol (438 mL). Themixture was stirred at 75° C., and then let gradually cool to 55° C. Tothe mixture was added dropwise water (657 mL). The mixture was stirredfor 1 hour, and then cooled to 15° C. over 3 hours. The resulted solidwas collected by filtration and washed with isopropanol:water (1:2)twice, and dried under reduced pressure to give the titled compound (133g).

1H-NMR (400 MHz, CDCl₃) δ: 7.68-7.66 (3H, m), 7.49 (2H, d, J=8.5 Hz),4.75-4.71 (1H, m), 4.22 (1H, dd, J=12.5, 4.3 Hz), 3.95 (1H, dd, J=12.5,7.6 Hz), 1.67 (3H, d, J=6.1 Hz).

Reference Example 5:(7S)-3-iodo-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

To a solution of the compound of Reference example 2 (5.15 g) in aceticacid (85 mL) was added 1,3-diiodo-5,5-dimethylhydantoin (10.35 g). Thereaction solution was stirred at 100° C. for 4 hours, and then let coolto room temperature. To the solution was added saturated aqueous sodiumthiosulfate solution. The mixture was extracted with chloroform:ethanol(4:1) twice, and then the organic layers were dried over anhydroussodium sulfate, filtered, and concentrated under reduced pressure togive the titled compound (11.06 g).

¹H-NMR (400 MHz, DMSO-d₆) δ: 7.93 (1H, s), 4.54-4.47 (1H, m), 3.66-3.61(1H, m), 3.33-3.29 (1H, m), 1.42 (3H, d, J=6.1 Hz).

LC-MS, m/z; 278[M+H]⁺ retention time; 0.567 min

Reference Example 6: imidazo[1,2-a]pyridin-6-ylboronic acid

A mixture of bis(pinacolato)diboron (3.74 g),6-bromoimidazo[1,2-a]pyridine (2.23 g),1,1′-bis(diphenylphosphino)ferrocenepalladium (II) chloride (0.924 g),and potassium acetate (2.78 g) in toluene (16 mL) was heated to refluxwith stirring for 2 hours. The reaction mixture was let cool to roomtemperature, and then filtered through Celite. The filtrate wasconcentrated under reduced pressure to give a crude product of thetitled compound. LC-MS, m/z; 163[M+H]⁺ retention time; 0.243 min

Reference Example 7:(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 5 (2.41 g), the compoundof Reference example 6 (1.83 g),palladium acetate (195 mg), X-phos (830mg), and potassium carbonate (2.41 g) in 1,2-dimethoxyethane (16mL)/water (8 mL) was heated to reflux with stirring for 4 hours. Thereaction mixture was let cool to room temperature, and then diluted withethyl acetate, and filtered through Celite. To the filtrate was addedwater, and the mixture was separated into layers. The organic layer waswashed with brine, and then dried over anhydrous sodium sulfate,filtered, and concentrated under reduced pressure. The resulted residuewas purified by amino silica gel column chromatography(chloroform/methanol) to give the titled compound (693.9 mg) LC-MS, m/z;268[M+H]⁺ retention time; 0.376 min

Reference Example 8:{(7S)-7-methyl-4-oxo-5-[4-(trifluoromethyl)phenyl]-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazin-3-yl}boronicacid

To a solution of the compound of Reference example 4 (10.00 g) and2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (9.60 mL) in THF(100 mL) was added dropwise isopropylmagnesium chloride-lithium chloridecomplex (42.7 mL) at −25° C. The reaction mixture was stirred at −25° C.for 30 minutes, and then thereto was added saturated aqueous ammoniumchloride solution. The mixture was extracted with ethyl acetate. Theorganic layer was washed with brine, and then dried over anhydroussodium sulfate, filtered, and concentrated under reduced pressure. Theresulted residue was purified by silica gel column chromatography(hexane/ethyl acetate) to give the titled compound (9.12 g) LC-MS, m/z;340[M+H]⁺ retention time; 0.865 min

Reference Example 9:(2R)-1-{[4-(trifluoromethyl)phenyl]amino}propan-2-ol

To a mixture of 1-iodo-4-(trifluoromethyl)benzene (168 g),(R)-1-aminopropan-2-ol (116 g), and methanol (168 mL) was addedpotassium hydroxide (69.3 g) at 20° C. with stirring, and the mixturewas stirred. Exotherm was cooled to 20° C., and to the mixture was addedcopper (I) chloride (6.11 g). The mixture was warmed to 30° C. andstirred for 3 hours, and then stirred at 20° C. for 15 hours. Methanolwas removed under reduced pressure, and to the residue were added water(880 mL), 28% ammonia water (220 mL), and toluene (880 mL). The mixturewas stirred for 30 minutes, and then separated into layers. The toluenelayer was washed with water (880 mL), and then concentrated underreduced pressure to give the titled compound (130 g).

1H-NMR (400 MHz, CDCl₃) δ: 7.39 (d, 2H, J=8.2 Hz), 6.66 (d, 2H, J=8.2Hz), 4.09-4.01 (m, 1H), 3.25 (dd, 1H, J=3.0, 12.8 Hz), 3.03 (dd, 1H,J=7.9, 12.8 Hz), 1.27 (d, 3H, J=6.7 Hz)

Reference Example 10: methyl4-bromo-1-{(2S)-1-[4-(trifluoromethyl)anilino]propan-2-yl}-1H-pyrazole-5-carboxylate

To a mixture of the compound of Reference example 9 (3.03 g),diisopropyl azodicarboxylate (2.93 g), methyl4-bromo-1H-pyrazole-5-carboxylate (2.83 g), and tetrahydrofuran (18 mL)was added triphenylphosphine (3.81 g) with stirring at ice temperature,and the mixture was stirred for 1.5 hours at ice temperature and for 22hours at 20° C. The reaction solution was concentrated and purified bycolumn chromatography (silica gel, hexane/ethyl acetate=8/1 to 5/1) togive the titled compound (2.38 g). 1H-NMR (400 MHz, CDCl₃) δ: 7.55 (s,1H), 7.35 (d, 2H, J=8.5 Hz), 6.52 (d, 2H, J=8.5 Hz), 5.57-5.52 (m, 1H),4.26 (br, 1H), 3.78 (s, 3H), 3.67-3.59 (m, 1H), 3.50-3.44 (m, 1H), 1.53(d, 3H, J=6.7 Hz)

Reference Example 11:4-bromo-1-{(2S)-1-[4-(trifluoromethyl)anilino]propan-2-yl}-1H-pyrazole-5-carboxylicacid

To a mixture of the compound of Reference example 10 (406 mg) andmethanol (2 mL) was added 1 mol/L aqueous sodium hydroxide solution (1.5mL), and the mixture was stirred at room temperature for 24 hours. Thereaction solution was cooled with ice, acidified with 5% aqueouspotassium hydrogensulfate solution, and extracted with ethyl acetate.The organic layer was dried over anhydrous sodium sulfate, and thenconcentrated under reduced pressure to give the titled compound (392mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 13.84 (brs, 1H), 7.75 (s, 1H), 7.32 (d, 2H,J=8.9 Hz), 6.64 (d, 2H, J=8.9 Hz), 6.44 (br, 1H), 5.52-5.44 (m, 1H),3.53-3.47 (m, 1H), 3.40-3.35 (m, 1H), 1.43 (d, 3H, J=6.7 Hz).

Reference Example 12:(7S)-3-bromo-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

Synthesis-1: To a mixture of the compound of Reference example 11 (392mg) and toluene (3 mL) was added p-toluenesulfonic acid monohydrate (16mg), and the mixture was stirred at 100° C. for 12 hours. The reactionsolution was cooled to 20° C., and thereto was added saturated aqueoussodium hydrogen carbonate solution. The mixture was extracted withtoluene. The organic layer was dried over sodium sulfate, and thenconcentrated under reduced pressure to give the titled compound (356mg).Synthesis-2: To a mixture of the compound of Reference example 10 (406mg) and toluene (3 mL) was added p-toluenesulfonic acid monohydrate (16mg), and the mixture was stirred at 100° C. for 8 hours. The areapercentage of liquid chromatography showed the ratio of product/startingmaterial=15/82.

¹H-NMR (400 MHz, CDCl₃) δ: 7.67 (d, 2H, J=8.5 Hz), 7.59 (s, 1H), 7.49(d, 2H, J=8.5 Hz), 4.73-4.65 (m, 1H), 4.20 (dd, 1H, J=4.3, 12.8 Hz),3.95 (dd, 1H, J=7.3, 12.8 Hz), 1.67 (d, 3H, J=6.7 Hz).

Reference Example 13:(7S)-3-(3-iodoimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A solution of the compound of Example 1 (386 mg) and1,3-diiodo-5,5-dimethylhydantoin (178 mg) in acetic acid (4 mL) wasstirred at room temperature for 5 hours. To the reaction solution wasadded saturated aqueous sodium thiosulfate solution, and the mixture wasextracted with ethyl acetate. The organic layer was washed withsaturated sodium hydrogen carbonate solution and brine, and then driedover anhydrous sodium sulfate, filtered, and concentrated under reducedpressure. The resulted residue was purified by silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (403mg).

¹H-NMR (400 MHz, DMSO-D₆) δ: 9.02 (1H, d, J=1.2 Hz), 8.14 (1H, s), 7.82(2H, d, J=8.5 Hz), 7.70-7.59 (5H, m), 4.85-4.83 (1H, m), 4.38 (1H, dd,J=12.8, 4.3 Hz), 4.12-4.07 (1H, m), 1.60 (3H, d, J=6.7 Hz).

Reference Example 14:(7S)-3-(3-ethenylimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 13 (219 mg),4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane (0.14 mL),tetrakis(triphenylphosphine)palladium (0) (47.1 mg), and potassiumcarbonate (130 mg) in 1,2-dimethoxyethane (2 mL) and water (1 mL) washeated to reflux with stirring for 4 hours. The reaction mixture was letcool to room temperature, and then diluted with ethyl acetate andfiltered through Celite. To the filtrate was added saturated aqueoussodium hydrogen carbonate solution, and the mixture was separated intolayers. The organic layer was washed with brine, and then dried overanhydrous sodium sulfate, filtered, and concentrated under reducedpressure. The resulted residue was purified by amino silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (87.8mg).

LC-MS, m/z; 438[M+H]⁺ retention time; 0.805 min

Reference Example 15:(7S)-7-methyl-3-{3-[(1Z)-prop-1-en-1-yl]imidazo[1,2-a]pyridin-6-yl}-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 13 (210 mg) was treated withcis-propenylboronic acid (67.1 mg) in a similar manner to Referenceexample 14 to give the titled compound (114.1 mg).

LC-MS, m/z; 452[M+H]⁺ retention time; 0.805 min

Reference Example 16:(7S)-5-(4-fluoro-3-methylphenyl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 2 (1.05 g) was treated with4-bromo-1-fluoro-2-methylbenzene (1.58 g) in a similar manner toReference example 3 to give the titled compound (1.80 g).

¹H-NMR (400 MHz, CDCl₃) δ: 7.57 (1H, d, J=1.8 Hz), 7.16 (1H, dd, J=6.7,3.1 Hz), 7.11-7.07 (1H, m), 7.04-7.02 (1H, m), 6.92 (1H, d, J=1.8 Hz),4.70-4.62 (1H, m), 4.12 (1H, dd, J=12.8, 4.3 Hz), 3.84 (1H, dd, J=12.8,7.3 Hz), 2.27 (3H, d, J=1.8 Hz), 1.66 (3H, d, J=6.7 Hz).

Reference Example 17:(7S)-5-(4-fluoro-3-methylphenyl)-3-iodo-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 16 (1.70 g) was treated in a similarmanner to Reference example 4 to give the titled compound (2.00 g).

1H-NMR (400 MHz, CDCl₃) δ: 7.62 (1H, s), 7.18 (1H, dd, J=6.7, 2.4 Hz),7.10-7.06 (1H, m), 7.03-7.01 (1H, m), 4.72-4.64 (1H, m), 4.13 (1H, dd,J=12.8, 4.3 Hz), 3.85 (1H, dd, J=12.8, 7.3 Hz), 2.27 (3H, d, J=1.8 Hz),1.64 (3H, d, J=6.1 Hz).

Reference Example 18:(7S)-5-(4-fluoro-3-methylphenyl)-3-(3-iodoimidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Example 17 (40.0 mg) was treated in a similar manner toReference example 13 to give the titled compound (39.4 mg).

1H-NMR (400 MHz, CDCl₃) δ: 8.59-8.59 (1H, m), 7.77 (1H, s), 7.65 (1H,s), 7.54-7.53 (2H, m), 7.16 (1H, dd, J=6.9, 2.7 Hz), 7.12-7.08 (1H, m),7.04-6.99 (1H, m), 4.77-4.74 (1H, m), 4.20 (1H, dd, J=12.8, 4.1 Hz),3.90 (1H, dd, J=12.8, 7.1 Hz), 2.26 (3H, d, J=1.8 Hz), 1.73 (3H, d,J=6.4 Hz).

Reference Example 19

A mixture of 6-bromoimidazo[1,2-a]pyridine (151.72 g),bis(pinacolato)diboron (235 g),1,1′-bis(diphenylphosphino)ferrocenepalladium (II)chloride-dichloromethane adduct (62.9 g), and potassium acetate (189 g)in 1,2-dimethoxyethane (1.59 L) was heated to reflux with stirring for4.5 hours. The reaction mixture was let cool to room temperature, andthen the precipitated solid was collected by filtration and washed with1,2-dimethoxyethane (200 ml). To the resulted solid were added water(500 ml) and hexane (500 ml), and the mixture was suspended withstirring at room temperature for 30 minutes. The resulted solid wascollected by filtration and washed with 1,2-dimethoxyethane (400 ml)three times to give the titled compound (145.1 g).

1H-NMR (400 MHz, CDCl₃) δ: 8.55 (1H, t, J=1.2 Hz), 7.62-7.56 (3H, m),7.44 (1H, dd, J=9.2, 1.2 Hz), 1.35 (13H, s).

Example 1:(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

Synthesis-1: A mixture of the compound of Reference example 4 (1.15 g),the compound of Reference example 6 (661 mg), palladium acetate (61.1mg), X-phos (259 mg), and potassium carbonate (752 mg) in1,2-dimethoxyethane (6 mL)/water (3 mL) was heated to reflux withstirring for 3 hours. The reaction mixture was let cool to roomtemperature, and then diluted with ethyl acetate and filtered throughCelite. To the filtrate was added water, and the mixture was separatedinto layers. The organic layer was washed with brine, and then driedover anhydrous sodium sulfate, filtered, and concentrated under reducedpressure. The resulted residue was purified by amino silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (551.5mg).Synthesis-2: A mixture of the compound of Reference example 12 (177 mg),the compound of Reference example 6 (92 mg), potassium carbonate (196mg), tetrakis(triphenylphosphine)palladium (0) (27 mg), 1,4-dioxane (1.9mL), and water (0.47 mL) was stirred at 90° C. for 3.5 hours. Themixture was cooled to 20° C., and thereto was added brine. The mixturewas extracted with ethyl acetate. The organic layer was dried overanhydrous sodium sulfate, and then concentrated under reduced pressure.The resulted residue was stirred in ethyl acetate (about 1.5 mL) at roomtemperature, and the resulted solid was collected by filtration. Thesolid was washed with ethyl acetate (about 0.5 mL) to give the titledcompound (102 mg).Synthesis-3: A mixture of the compound of Reference example 4 (116 g),the compound of Reference example 6 (67.0 g), palladium acetate (6.20g), X-phos (26.3 g), and potassium carbonate (76 g) in1,2-dimethoxyethane (700 mL)/water (350 mL) was heated to reflux withstirring for 3 hours. The reaction mixture was let cool to roomtemperature, and then thereto were added ethyl acetate (500 mL) and 2mol/L hydrochloric acid (1000 mL). The mixture was stirred at roomtemperature for 30 minutes. The mixture was filtered through Celite, andthe residue was washed with ethyl acetate (500 mL), and then thefiltrate was separated into layers. The organic layer was washed with 2mol/L hydrochloric acid (500 mL) twice, and the aqueous layers werecombined, and adjusted to pH 9 by addition of 10 mol/L aqueous sodiumhydroxide solution. The aqueous layer was extracted with chloroform (500mL) three times, and then washed with brine, and then dried overanhydrous sodium sulfate, filtered, and concentrated under reducedpressure. To the residue (125.3 g) was added ethanol (1253 mL), and themixture was heated to reflux with stirring for 30 minutes. To themixture was added water (626 mL), and the mixture was heated to refluxwith stirring. The mixture was let cool to room temperature, and thenthe resulted solid was collected by filtration and washed with ethylacetate. To the resulted solid (44.4 g) was added ethyl acetate (666mL), and the mixture was heated to reflux with stirring for 30 minutes.The mixture was let cool to room temperature, and then the resultedsolid was collected by filtration, washed with ethyl acetate, and driedunder reduced pressure to give the titled compound (39.77 g).Synthesis-4: A mixture of the compound of Reference example 4 (28.5 g),the compound of Reference example 19 (33.5 g), palladium acetate (1.519g), S-phos (5.56 g), and potassium carbonate (18.70 g) in1,2-dimethoxyethane (100 mL)/water (50 mL) was heated to reflux withstirring for 3 hours. The reaction mixture was let cool to roomtemperature, and then diluted with chloroform (180 mL)/methanol (20 mL)and filtered through Celite, and washed with chloroform (450mL)/methanol (50 mL). To the resulted filtrate was added aqueous sodiumhydrogen carbonate solution, and the mixture was separated into layers.The organic layer was washed with brine, and then dried over anhydroussodium sulfate, filtered, and concentrated under reduced pressure. Theresulted residue was purified by silica gel column chromatography (ethylacetate/methanol) to give a solid. The resulted solid (21.23 g) waswashed with ethyl acetate (210 ml), and collected by filtration. To asolution of the resulted solid (13.65 g) in chloroform (117 mL)/methanol(13 mL) was added activated carbon (trade name “Kyoryoku Shirasagi”)(6.5 g), and the mixture was stirred at room temperature for 1 hour.Then, to the mixture was added Argoregin MP-TMT (6.5 g), and the mixturewas stirred at room temperature for additional 1 hour. The resultedsolution was filtered through Celite and washed with chloroform (720mL)/methanol (80 mL), and then the filtrate was concentrated underreduced pressure to give the titled compound (12.03 g).

1H-NMR (400 MHz, CDCl₃) δ: 8.89 (1H, d, J=1.8 Hz), 7.80 (1H, s), 7.70(2H, d, J=8.5 Hz), 7.59-7.55 (3H, m), 7.48 (2H, d, J=8.5 Hz), 7.40 (1H,dd, J=9.8, 1.8 Hz), 4.80-4.75 (1H, m), 4.27 (1H, dd, J=12.5, 4.0 Hz),3.99 (1H, dd, J=12.5, 7.3 Hz), 1.74 (3H, d, J=6.1 Hz).

[Crystalline Form I]

Major diffraction peaks: 2θ (°)=4.5, 8.5, 8.9, 10.1, 13.4, 16.9, 18.2,18.6, 22.7, 23.8

Characteristic diffraction peaks: 2θ (°)=4.5, 8.5, 8.9, 10.1, 13.4, 16.9

Preparation of a hydrochloride salt of the compound of Example 1

To a solution of the compound of Example 1 (10.8 g) in chloroform (100mL) was added 4 mol/L hydrochloric acid-ethyl acetate (200 mL), and themixture was stirred at room temperature for 5 minutes. The reactionmixture was concentrated under reduced pressure, and then to the residuewas added ethanol (100 mL). The mixture was heated to reflux withstirring for 30 minutes. To the mixture was added hexane (50 mL), andthe mixture was heated to reflux with stirring for additional 1 hour.The mixture was let cool to room temperature, and then the resultedsolid was collected by filtration, washed with ethanol/hexane (1/2), anddried under reduced pressure to give a hydrochloride salt of thecompound of Example 1 (10.0 g).

¹H-NMR (400 MHz, DMSO-d₆) δ: 9.37 (1H, s), 8.39 (1H, d, J=1.8 Hz), 8.28(1H, dd, J=9.4, 1.5 Hz), 8.20 (1H, d, J=1.8 Hz), 8.12 (1H, s), 7.98 (1H,d, J=9.1 Hz), 7.83 (2H, d, J=8.5 Hz), 7.68 (2H, d, J=8.5 Hz), 4.89-4.87(1H, m), 4.40 (1H, dd, J=12.8, 6.4 Hz), 4.14 (1H, dd, J=12.8, 7.6 Hz),1.61 (3H, d, J=6.1 Hz).

[Crystalline Form II]

Major diffraction peaks: 2θ (°)=5.7, 8.7, 9.5, 11.0, 11.3, 12.7, 13.6,15.3, 15.5, 16.6, 21.5

Characteristic diffraction peaks: 2θ (°)=5.7, 8.7, 9.5, 11.0, 11.3, 15.3

Preparation of a phosphate salt of the compound of Example 1

To a suspension of the compound of Example 1 (8.80 g) in ethyl acetate(150 mL) was added phosphoric acid (4.38 mL), and the mixture was heatedto reflux with stirring for 1 hour. The mixture was let cool to roomtemperature, and then the resulted solid was collected by filtration,washed with ethyl acetate, and dried under reduced pressure to give a2.5 phosphate salt of the compound of Example 1 (14.18 g). 1H-NMR (400MHz, DMSO-d₆) δ: 9.05 (1H, s), 8.02 (1H, s), 7.97 (1H, s), 7.81 (2H, d,J=8.5 Hz), 7.67 (2H, d, J=8.5 Hz), 7.62-7.58 (3H, m), 4.85-4.82 (1H, m),4.37 (1H, dd, J=12.8, 4.3 Hz), 4.10 (1H, dd, J=12.8, 7.9 Hz), 1.59 (3H,d, J=6.1 Hz).

[Crystalline Form III]

Major diffraction peaks: 2θ (°)=6.1, 6.9, 8.9, 9.8, 12.1, 13.4, 13.7,18.0, 18.2, 20.6

Characteristic diffraction peaks: 2θ (°)=6.1, 8.9, 9.8, 12.1, 13.4, 13.7

CHN elemental analysis: C₂₁H₁₆F₃N₅O.2.5 H₃PO₄; theoretical value: C,38.43%; H, 3.61%; N, 10.67%, measured value: C, 38.29%; H, 3.59%; N,10.54%.

Ion analysis: phosphate ion (PO₄ ³⁻) of C₂₁H₁₆F₃N₅O.2.5 H₃PO₄;theoretical value: 36.13%, measured value: 35.94%, 35.90%.

Example 2:(7S)-3-(imidazo[1,2-a]pyrazin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 4 (848 mg) was treated withimidazo[1,2-a]pyrazin-6-ylboronic acid (492 mg) in a similar manner toExample 1 to give the titled compound (4 mg).

¹H-NMR (400 MHz, CDCl₃) δ: 9.71 (1H, s), 9.09 (1H, s), 8.40 (1H, s),7.76-7.74 (3H, m), 7.66 (1H, s), 7.52 (2H, d, J=7.9 Hz), 4.82-4.80 (1H,m), 4.29 (1H, dd, J=12.2, 3.7 Hz), 3.98 (1H, dd, J=12.2, 6.7 Hz), 1.75(3H, d, J=6.1 Hz).

Example 3:(⁷S)-5-(3-chloro-4-fluorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 7 (300 mg),4-bromo-2-chloro-1-fluorobenzene (0.204 mL), copper iodide (64.1 mg),N,N′-dimethylethylenediamine (0.109 mL), and potassium carbonate (310mg) in toluene (2.5 mL) was heated to reflux with stirring for 5 hours.The reaction mixture was let cool to room temperature, and then theretowas added 28% ammonia water. The mixture was extracted with ethylacetate. The organic layer was washed with saturated aqueous ammoniumchloride solution, saturated aqueous sodium hydrogen carbonate solution,and brine, and then dried over anhydrous sodium sulfate, filtered, andconcentrated under reduced pressure. The resulted residue was purifiedby amino silica gel column chromatography (hexane/ethyl acetate) to givethe titled compound (263.3 mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 9.38 (1H, s), 8.40 (1H, d, J=1.8 Hz), 8.28(1H, dd, J=9.5, 1.5 Hz), 8.19 (1H, d, J=1.8 Hz), 8.12 (1H, s), 7.98 (1H,d, J=9.2 Hz), 7.75 (1H, dd, J=6.7, 2.4 Hz), 7.55-7.46 (2H, m), 4.88-4.83(1H, m), 4.32 (1H, dd, J=12.8, 4.3 Hz), 4.05 (1H, dd, J=12.8, 7.6 Hz),1.60 (3H, d, J=6.1 Hz).

Examples 4 to 9

Compounds of corresponding Reference examples were treated according tothe method of Example 3 to give the compounds of Examples 4 to 9 asshown in the following table.

Chemical Example structure Instrumental analysis data 4

¹H-NMR (400 MHz, DMSO-d₆) δ: 9.03 (1H, s), 8.01 (1H, s), 7.94 (1H, s),7.65 (2H, d, J = 8.5 Hz), 7.58 (2H, d, J = 8.5 Hz), 7.55 (3H, d, J = 2.4Hz), 7.06 (1H, t, J = 55.8 Hz), 4.84-4.80 (1H, m), 4.34 (1H, dd, J =12.8, 4.3 Hz), 4.07 (1H, dd, J = 12.8, 7.3 Hz), 1.59 (3H, d, J = 6.7Hz). 5

¹H-NMR (400 MHz, CDCl₃) δ: 8.88 (1H, d, J = 1.8 Hz), 7.79 (1H, s),7.59-7.57 (3H, m), 7.46-7.44 (1H, m), 7.41-7.38 (1H, m), 7.21 (1H, dd, J= 9.8, 2.4 Hz), 7.11- 7.08 (1H, m), 4.79-4.74 (1H, m), 4.21 (1H, dd, J =12.8, 4.3 Hz), 3.93 (1H, dd, J = 12.8, 7.3 Hz), 1.73 (3H, d, J = 6.7Hz). 6

¹H-NMR (400 MHz, CDCl₃) δ: 8.93 (1H, s), 7.79 (1H, s), 7.59-7.55 (3H,m), 7.42-7.39 (3H, m), 7.28 (2H, d, J = 8.5 Hz), 4.78-4.72 (1H, m), 4.21(1H, dd, J = 12.8, 4.3 Hz), 3.92 (1H, dd, J = 12.8, 7.3 Hz), 1.72 (3H,d, J = 6.7 Hz). 7

HPLC Rt = 4.489 LC-MS, m/z; 384[M + H]⁺, Rt: 1.558 min 8

¹H-NMR (400 MHz, CDCl₃) δ: 8.93 (1H, s), 7.80 (1H, s), 7.59-7.53 (3H,m), 7.41 (1H, dd, J = 9.4, 1.5 Hz), 7.12-7.10 (2H, m), 7.02 (1H, dd, J =8.5, 2.4 Hz), 4.78- 4.76 (1H, m), 4.20 (1H, dd, J = 12.8, 4.3 Hz), 3.90(1H, dd, J = 12.8, 7.3 Hz), 1.73 (3H, d, J = 6.1 Hz). 9

¹H-NMR (400 MHz, CDCl₃) δ: 8.93 (1H, s), 7.79 (1H, s), 7.59-7.55 (3H,m), 7.43-7.33 (3H, m), 7.20 (2H, d, J = 8.5 Hz), 6.50 (1H, t, J = 73.4Hz), 4.78-4.74 (1H, m), 4.22 (1H, dd, J = 12.8, 4.3 Hz), 3.92 (1H, dd, J= 12.8, 7.3 Hz), 1.73 (3H, d, J = 6.1 Hz).

The following show the chemical names of the compounds of Examples 4 to9.

-   Example 4:    (7S)-5-[4-(difluoromethyl)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 5:    (7S)-5-(4-chloro-3-fluorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 6:    (7S)-5-(4-chlorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 7:    (7S)-5-(5-chlorothiophen-2-yl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 8:    (7S)-5-(2,2-difluoro-1,3-benzodioxol-5-yl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 9:    (7S)-5-[4-(difluoromethoxy)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one-   Example 10:    (7S)-3-(2-aminoimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of 6-bromoimidazo[1,2-a]pyridin-2-amine (299 mg), the compoundof Reference example 8 (318.9 mg), palladium acetate (21.1 mg), X-phos(90.0 mg), and potassium carbonate (260 mg) in DMF (2 mL) was stirred at105° C. for 6 hours. The reaction mixture was let cool to roomtemperature, and then diluted with ethyl acetate and filtered throughCelite. To the filtrate was added water, and the mixture was separatedinto layers. The organic layer was washed with water twice and brine,and then dried over anhydrous sodium sulfate, filtered, and concentratedunder reduced pressure. The resulted residue was purified by aminosilica gel column chromatography (hexane/ethyl acetate) to give thetitled compound (5.10 mg).

LC-MS, m/z; 427[M+H]⁺ retention time; 0.675 min HPLC Rt=4.438 min

Example 11:(7S)-3-(3-aminoimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 8 (372 mg) was treated with6-bromoimidazo[1,2-a]pyridin-3-amine (302 mg) in a similar manner toExample 10 to give the titled compound (87.5 mg).

1H-NMR (400 MHz, CDCl₃) δ: 8.64 (1H, d, J=1.8 Hz), 7.79 (1H, s), 7.68(2H, d, J=8.5 Hz), 7.49-7.46 (3H, m), 7.33 (1H, dd, J=9.2, 1.8 Hz), 7.16(1H, s), 4.79-4.73 (1H, m), 4.26 (1H, dd, J=0.12.8, 4.3 Hz), 3.98 (1H,dd, J=12.8, 7.3 Hz), 3.25 (2H, brs), 1.73 (3H, d, J=6.7 Hz).

Example 12:(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[5-(trifluoromethyl)pyridin-2-yl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of 2-chloro-5-(trifluoromethyl)pyridine (345 mg), the compoundof Reference example 7 (339 mg), tetrakis(triphenylphosphine)palladium(0) (147 mg), cesium carbonate (826 mg), and4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (147 mg) in 1,4-dioxane(3 mL) was heated to reflux with stirring for 5 hours. The reactionmixture was let cool to room temperature, and then diluted with ethylacetate and filtered through Celite. To the filtrate was added saturatedaqueous ammonium chloride solution, and the mixture was separated intolayers. The organic layer was washed with brine, and then dried overanhydrous sodium sulfate, filtered, and concentrated under reducedpressure. The resulted residue was purified by amino silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (414.9mg).

LC-MS, m/z; 427[M+H]⁺ retention time; 0.675 min

¹H-NMR (400 MHz, CDCl₃) δ: 8.71 (2H, dd, J=11.0, 1.8 Hz), 8.21 (1H, d,J=9.2 Hz), 7.93 (1H, dd, J=8.9, 2.1 Hz), 7.77 (1H, s), 7.63-7.60 (3H,m), 7.40 (1H, dd, J=9.2, 1.8 Hz), 4.76-4.69 (2H, m), 4.39-4.34 (1H, m),1.72 (3H, d, J=6.7 Hz).

Example 13:(7S)-3-(3-fluoroimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Example 1 (544 mg) and1-fluoro-4-methyl-1,4-diazoniabicyclo[2,2,2]octanebis(tetrafluoroborate) (634 mg) in acetonitrile (6 mL) was stirred atroom temperature for 6 hours. To the reaction mixture was addedsaturated aqueous sodium thiosulfate solution, and the mixture wasextracted with ethyl acetate. The organic layer was washed withsaturated aqueous sodium hydrogen carbonate solution and brine, and thendried over anhydrous sodium sulfate, filtered, and concentrated underreduced pressure. The resulted residue was purified by silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (21.8mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 8.85 (1H, s), 8.11 (1H, s), 7.82 (2H, d,J=8.5 Hz), 7.68 (2H, d, J=8.5 Hz), 7.60 (1H, dd, J=9.8, 1.8 Hz),7.52-7.51 (1H, m), 7.35 (1H, d, J=7.3 Hz), 4.85-4.83 (1H, m), 4.37 (1H,dd, J=12.8, 4.3 Hz), 4.09 (1H, dd, J=12.8, 7.3 Hz), 1.59 (3H, d, J=6.1Hz).

Example 14:(7S)-7-methyl-3-(3-methylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 13 (219 mg),methylboronic acid (73.2 mg), tetrakis(triphenylphosphine)palladium (0)(47.1 mg), and sodium hydroxide (48.9 mg) in 1,2-dimethoxyethane (2 mL)and water (1 mL) was heated to reflux with stirring for 4 hours. Thereaction mixture was let cool to room temperature, and then diluted withchloroform and filtered through Celite. To the filtrate was addedsaturated aqueous sodium hydrogen carbonate solution, and the mixturewas separated into layers. The organic layer was washed with brine, andthen dried over anhydrous sodium sulfate, filtered, and concentratedunder reduced pressure. The resulted residue was purified by aminosilica gel column chromatography (hexane/ethyl acetate) to give thetitled compound (20.3 mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 8.75 (1H, s), 8.07 (1H, s), 7.82 (2H, d,J=7.9 Hz), 7.68 (2H, d, J=7.9 Hz), 7.54-7.52 (2H, m), 7.35 (1H, s),4.84-4.83 (1H, m), 4.39-4.38 (1H, m), 4.09 (1H, dd, J=12.2, 7.9 Hz),2.43 (3H, s), 1.59 (3H, d, J=6.1 Hz).

Example 15:(7S)-3-(3-ethylimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 14 (87 mg) and 10%palladium-carbon (166 mg) in methanol (7 mL) was stirred under hydrogenatmosphere at room temperature for 3 hours. The reaction mixture wasfiltered through Celite, and the filtrate was concentrated under reducedpressure. The resulted residue was purified by amino silica gel columnchromatography (hexane/ethyl acetate) to give the titled compound (46.9mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 8.81 (1H, s), 8.07 (1H, s), 7.82 (2H, d,J=8.5 Hz), 7.68 (2H, d, J=8.5 Hz), 7.56-7.50 (2H, m), 7.36 (1H, s),4.84-4.82 (1H, m), 4.38 (1H, dd, J=12.8, 4.3 Hz), 4.08 (1H, dd, J=12.8,7.3 Hz), 2.83 (2H, a, J=7.5 Hz), 1.59 (3H, d, J=6.7 Hz), 1.30 (3H, t,J=7.5 Hz).

Example 16:(7S)-7-methyl-3-(3-propylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Reference example 15 (114.1 mg) was treated in a similarmanner to Example 15 to give the titled compound (66.7 mg).

1H-NMR (400 MHz, DMSO-d₆) δ: 8.81 (1H, s), 8.06 (1H, s), 7.81 (2H, d,J=8.5 Hz), 7.68 (2H, d, J=8.5 Hz), 7.52 (2H, s), 7.36 (1H, s), 4.85-4.81(1H, m), 4.37 (1H, dd, J=13.1, 4.0 Hz), 4.08 (1H, dd, J=13.1, 7.6 Hz),2.82 (2H, t, J=7.3 Hz), 1.74-1.66 (2H, m), 1.59 (3H, d, J=6.7 Hz), 0.95(3H, t, J=7.3 Hz).

Example 17:(7S)-5-(4-fluoro-3-methylphenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

A mixture of the compound of Reference example 17 (161.8 mg), thecompound of Reference example 6 (109 mg), palladium acetate (9.4 mg),S-phos (34.5 mg), and potassium carbonate (116 mg) in1,2-dimethoxyethane (1.4 mL)/water (0.7 mL) was heated to reflux withstirring for 2 hours. The reaction mixture was let cool to roomtemperature, and then diluted with ethyl acetate and filtered throughCelite. To the filtrate was added saturated aqueous sodium hydrogencarbonate solution, and the mixture was separated into layers. Theorganic layer was washed with brine, and then dried over anhydroussodium sulfate, filtered, and concentrated under reduce pressure. Theresulted residue was purified by silica gel column chromatography(hexane/ethyl acetate) to give the titled compound (109 mg).

1H-NMR (400 MHz, CDCl₃) δ: 9.01 (1H, s), 7.80 (1H, s), 7.62-7.57 (3H,m), 7.46 (1H, dd, J=9.6, 1.4 Hz), 7.17-7.16 (1H, m), 7.10-7.07 (2H, m),4.77-4.73 (1H, m), 4.19 (1H, dd, J=12.8, 4.1 Hz), 3.89 (1H, dd, J=12.8,7.3 Hz), 2.28 (3H, d, J=1.8 Hz), 1.72 (3H, d, J=6.4 Hz).

Example 18:(7S)-3-(3-fluoroimidazo[1,2-a]pyridin-6-yl)-5-(4-fluoro-3-methylphenyl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

The compound of Example 17 (81.4 mg) was treated in a similar manner toExample 13 to give the titled compound (4.2 mg).

1H-NMR (400 MHz, CDCl₃) δ: 9.01 (1H, s), 8.12 (1H, d, J=9.8 Hz), 7.86(1H, d, J=9.2 Hz), 7.80 (1H, s), 7.43 (1H, d, J=6.1 Hz), 7.11-7.00 (3H,m), 4.75-4.74 (1H, m), 4.17 (1H, dd, J=12.8, 4.3 Hz), 3.87 (1H, dd,J=12.8, 7.0 Hz), 2.24 (3H, d, J=1.8 Hz), 1.70 (3H, d, J=6.1 Hz).

Example 19:(7S)-5-(4-fluoro-3-methylphenyl)-7-methyl-3-(3-methylimidazo[1,2-a]pyridin-6-yl)-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one

To a mixture of the compound of Reference example 18 (30.0 mg) andbis-(tri-tert-butylphosphine)palladium (0) (6.12 mg) in THF (1.2 mL) wasadded methylzinc chloride (59.8 μL, 2.0M THF solution), and the mixturewas stirred at room temperature for 5 hours. To the reaction mixture wasadded saturated aqueous ammonium chloride solution, and the mixture wasextracted with ethyl acetate twice. The organic layers were combined,dried over anhydrous sodium sulfate, filtered, and concentrated underreduced pressure. The resulted residue was purified by amino silica gelcolumn chromatography (hexane/ethyl acetate) to give the titled compound(16 mg).

1H-NMR (400 MHz, CDCl₃) δ: 9.14 (1H, s), 8.18 (1H, d, J=9.1 Hz), 7.90(1H, d, J=9.1 Hz), 7.83 (1H, s), 7.55 (1H, s), 7.11-7.00 (3H, m),4.76-4.74 (1H, m), 4.17 (1H, dd, J=12.8, 4.1 Hz), 3.86 (1H, dd, J=12.8,7.1 Hz), 2.52 (3H, s), 2.24 (3H, d, J=1.8 Hz), 1.70 (3H, d, J=6.4 Hz).

Tests

The following are pharmacological test methods and results for thepresent compound, but the present invention is not intended to belimited to these tests.

Test 1: Assessment with Human mGlu2 Receptor Stable Expressing Cells(1) Human mGlu2 Receptor Stable Expressing Cells

Human mGlu2 receptor stable expressing cells were prepared, and used forincubation. Specifically, human mGlu2 receptor gene was inserted intopcDNA4/TO (K1020-01, Life technologies, Carlsbad, Calif., USA), andintroduced into TR-expressed human kidney-derived HEK cells (cat#CCL-82.2, ATCC, USA), followed by screening with Geneticin (cat#10131-027, Life technologies, Carlsbad, Calif., USA), to obtain humanmGlu2 receptor stable expressing cells.

High glucose-DMEM media (cat #11995-065, Life technologies, Carlsbad,Calif., USA) containing 10% Dialysed-FBS (cat #26400-044, Lifetechnologies, Carlsbad, Calif., USA), 50 μg/mL Blasticidin S (cat#ANT-BL-1, Life technologies, Carlsbad, Calif., USA), and 2 mg/mL G418(cat #16513-84, nacalai tesque, Kyoto, Japan) were used for incubationon flasks for cell culture (cat #3133-150, AGC Thechno Glass, Shizuoka,Japan). During the incubation, cells were recovered by the treatmentwith TrypLE Express (cat #12604-013, Life technologies, Carlsbad,Calif., USA), followed by subculture, every three to four days.

Cells were recovered by an about 80% confluency in the treatment withTrypLE Express three to four days after the subculture, transientlytransfected with Ga16, apoaequorin, in media of Hanks (cat #14065-056,Life technologies, Carlsbad, Calif., USA)/20 mmol/L HEPES (cat#15630-080, Life technologies, Carlsbad, Calif., USA) Buffer (pH 7.4)containing 0.1% BSA (cat #12604-013, Life technologies, Carlsbad,Calif., USA) and 0.1 μg/mL Tetracycline (cat #33031-64, nacalai tesque,Kyoto, Japan), and then seeded on a 384-well plate (cat #781090, Greinerbio-one, Frickenhausen, Germany) in 1,500 cells/30 μL/well.

Coelentetrazine h (cat #S2011, Promega, Madison, Wis., USA) was added tothe plate (10 μl/well) so as to be a final concentration of 1 μmol/L onthe day after the seeding, and let stand for 4 hours or more at roomtemperature after centrifugation.

(2) Preparation of Test Compounds

A test compound was dissolved in DMSO so as to be a concentration 1000times higher than the assessment concentration. This DMSO solution wasdiluted with a medium (Hanks, 20 mmol/L HEPES, 0.1% BSA) to aconcentration 6 times higher than the assessment concentration.Glutamate was diluted with Hanks/20 mmol/L HEPES/0.1% BSA medium to aconcentration 6 times higher than EC₈₀ concentration.

(3) Assessment of mGlu2 Receptor Negative Allosteric Modulator Activity

Human mGlu2 receptor stable expressing cells were prepared andincubated. Luminescence signals by mGlu2 receptor stimulation weredetected with FDSS7000 (Hamamatsu Photonics). The compound solutionprepared above was added to a plate where cells and luminescentsubstrates were added (10 μl/well). After 120 seconds of the addition,EC₈₀ Glutamate-containing solution was added thereto (10 μl/well), andluminescence signals were measured for 300 seconds after the addition(center wavelength: 465 nm) for calculation of RLU (Integration). mGlu2receptor negative allosteric modulator activity of a compound wascalculated by (100-100×(RLU of each compound and concentration)/(RLU ofDMSO group)).

The present compound was assessed with the above biological test, andthe compounds with mGlu2 receptor negative allosteric modulator activitywere found out. mGlu2 receptor negative allosteric modulator activity(IC₅₀ value (nmol/L)) for each compound is shown in the following table.

mGluR2 NAM IC₅₀ (nM) or Example inhibition rate (%) 1 18 2 11 3 23 4 335 18 6 26 7 11 8 19 9 61 10 302 11 78 12 16 13 7.9 14 9.1 15 7.8 16 1317 17 18 6.9 19 16(4) Assessment of Time-Dependent mGlu2 Receptor Negative AllostericModulator Activity

Human mGlu2 receptor stable expressing cells are prepared and incubated.Luminescence signals by mGlu2 receptor stimulation are detected withFDSS7000 (Hamamatsu Photonics). The test compound solution prepared inthe above (2) is added to a plate where cells and luminescent substratesare added (10 μl/well). After 2, 15, 30, 60, and 120 minutes of theaddition, EC₈₀ Glutamate-containing solution is added thereto (10μl/well), and luminescence signals are measured for 300 seconds afterthe addition (center wavelength: 465 nm) for calculation of RLU(Integration). mGlu2 receptor negative allosteric modulator activity ofa compound at each time for addition is calculated by (100−100× (RLU ofeach compound and concentration)/(RLU of DMSO group)).

Test 2: Rat Forced Swimming Test

Existing antidepressants such as tricyclic antidepressants and serotoninreuptake inhibitors are known to shorten the immobility time in theforced swimming test in rats. This test system is used to assess theantidepressant-like effect of the present compound based on theimmobility time.

7-Week-old male Wistar rats are used for the rat forced swimming test.Specifically, animals are put into a tank filled with 5.8 L of tap water(water temperature 25±1° C.), and then forced to swim for 15 minutes(swimming training). After the swimming training, animals are wiped dryand return to the homecage. On the day after the swimming training, theswim test is performed for 5 minutes in the same manner as the swimmingtraining. Swimming behaviors of each individual are recorded with avideo camera through the side of tank. After the swimming test, animalsare wiped dry and return to the homecage. A test compound or a positivecontrol, imipramine, is suspended in a 0.5% methylcellulose solution fororal administration. A vehicle or a test compound is administered 15minutes after finishing the swim training and 2 hours before theswimming test. Imipramine is administered 15 minutes after finishing theswim training and 1 hour before the swimming test. Immobility is definedas the condition where an animal is floated without moving its forepawsand body in a tank, and the cumulative time of immobility during the5-minute swimming test is measured as the immobility time of theindividual. Student's t-test and Dunnett's multiple comparison are usedfor statistical processing.

Test 3: Enhancing Effect of Electrocortico γ-Frequency Band Power inRats

Changes in γ-frequency band power in electrocorticogram are consideredas an index of cortical activity, and mGluR2 antagonists, NAM, or NMDAreceptor antagonists (such as Ketamine) are known to enhance γ-frequencyband power. The present compound is assessed, whether to show enhancingγ-frequency band power.

The test is performed in the dark period by using male Wistar rats,which electroencephalogram measurement electrodes are implanted. Acompound is suspended in a 0.5% methylcellulose solution for oraladministration. Measurement of electroencephalogram and frequencyanalyses are carried out according to the method described in Progressin Neuro-Psychopharmacology & Biological Psychiatry 63 (2015) 6-13.Frequency of electroencephalogram is analyzed between 0.5 and 80 Hz, andthe frequency band between 30 and 80 Hz is defined as the γ frequency tocalculate the power value. The power change is measured every 1 houruntil 2 hours after administration as an index of the value beforeadministration as 100%. In view of duplicate measurement, the powerchanges are statistically compared using repeated measures two-way ANOVAfollowed by post hoc Dunnett tests.

Test 4: Assessment of MBT and Enzyme Inactivation Clearance AgainstCYP3A4

Cytochrome P450 (hereinafter called CYP) is the most important enzymegroup associated with drug metabolism, and most of pharmacokineticinteractions are based on the inhibition of the CYP activities. CYPincludes multiple molecular species. In particular, CYP3A4 is mostinvolved in drug metabolism in oxidation reaction with CYP, and accountsfor a major portion of CYPs existing in the liver.

CYP inhibition is generally divided into two types consisting of“reversible inhibition” and “irreversible inhibition (mechanism-basedinhibition: MBI)”. In particular, CYP inhibition based on the MBI isknown to have a possibility to cause severe side effects such ashepatotoxicity as well as drug-drug interactions (Curr Opin Drug DiscovDevel. 2010 January, 13(1), 66-77, Therapeutics and Clinical RiskManagement, 2005, 1(1), 3-13).

MBI and enzyme inactivation clearance against CYP3A4 were evaluated forexample compounds.

Inhibition effects and inhibition types of test compounds to CYP3A4 wereevaluated using human liver microsomes as an enzyme source and midazolamor testosterone as a substrate of CYP3A4. After metabolic reaction for30 minutes at 37° C., metabolites of CYP3A4 substrate in the presence orabsence of a test compound (at 4 concentrations) were measured byLC-MS/MS, and the inhibition rates were calculated from the ratios ofpeak area. IC₅₀ values were calculated from plots of test compoundconcentrations. It was known that when a test compound has MBIpotential, IC₅₀ value is lowered by starting metabolic reactions afterpreincubation in the presence of NADPH (cofactor). Therefore, it wasdetermined that there was MBI potential when the shift in IC₅₀ valuesdue to preincubation was 2-fold or more (Xenobiotica, 2009, 39(2),99-112).

When MBI potential was determined, k_(inact) (maximum inactivation rateconstant) and K₁ (inactivator concentration yielding a measuredinactivation rate at half of k_(inact)) were calculated by thenon-linear least-squares method. Enzyme inactivation clearance wascalculated according to the method described in Drug Metabolism andDisposition, 2011, 39(7), 1247-1254(CL_(int)=k_(inact)/K_(I)(ml/min/mmol)×CYP contents (pmol/mg protein)).

MBI and enzyme inactivation clearance against CYP3A4 for each Examplecompound are shown in the following table.

Enzyme inactivation clearance Example CYP3A4 MBI (μL/min/mg protein) 1N.D. 0 2 N.D. 0 3 N.D. 0 4 N.D. 0 5 N.D. 0 6 N.D. 0 7 4.5 2.146 8 2.20.601 9 N.D. 0 11 N.D. 0 12 2.2 0.159 13 N.D. 0 14 N.D. 0 15 N.D. 0 16N.D. 0 17 3.2 1.942 18 N.D. 0 19 N.D. 0

INDUSTRIAL APPLICABILITY

As explained above, the present compound shows negative allostericmodulation against Group II metabotropic glutamate (mGlu) receptors. Thepresent compound, is, therefore, useful as a therapeutic agent and/orpreventive agent for diseases involving metabotropic glutamate receptorsubtype 2 (mGluR2) and/or metabotropic glutamate receptor subtype 3(mGluR3).

1. A compound of Formula (1):

or a pharmaceutically acceptable salt thereof, wherein R¹ and R² areeach independently hydrogen atom, halogen atom, cyano, C₁₋₄ alkyl, orC₃₋₆ saturated carbocyclyl group, wherein the alkyl and the saturatedcarbocyclyl group are each independent and may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy, or alternatively,R¹ and R² may combine together with the carbon atom to which they attachto form a C₃₋₄ saturated carbocyclyl group, wherein the saturatedcarbocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy; Ring A is C₆₋₁₀ aromaticcarbocyclyl group, 4- to 10-membered saturated heterocyclyl group, or 5-to 10-membered aromatic heterocyclyl group; R³ and R⁴ are eachindependently hydrogen atom, halogen atom, cyano, hydroxy, C₁₋₆ alkyl,C₁₋₄ alkoxy, C₁₋₄ alkylthio, C₂₋₄ alkenyl, 4- to 6-membered saturatedheterocyclyl group, or 5- or 6-membered aromatic heterocyclyl group(wherein the alkyl, the alkoxy, the alkylthio, the saturatedheterocyclyl group, and the aromatic heterocyclyl group are eachindependent and may be optionally substituted with the same or different1 to 5 halogen atoms), C₃₋₆ saturated carbocyclyl group, or C₃₋₆cycloalkoxy, wherein the saturated carbocyclyl group and the cycloalkoxyare each independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom and C₁₋₄ alkyl; R⁵ and R⁶ are each independently hydrogenatom, halogen atom, cyano, hydroxy, C₁₋₆ alkyl, C₁₋₆ alkoxy, C₁₋₆alkylthio, 4- to 6-membered saturated heterocyclyl group (wherein thealkyl, the alkoxy, the alkylthio, and the saturated heterocyclyl groupare each independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms), C₃₋₆ cycloalkoxy, C₃₋₆saturated carbocyclyl group (wherein the cycloalkoxy and the saturatedcarbocyclyl group are each independent and may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄ alkoxyoptionally substituted with the same or different 1 to 5 halogen atoms),—N^(a)R^(b), —NR^(d)—C(O)—R^(c), —NR^(d)—C(O)—OR^(c),—NR^(d)—C(O)—NR^(a)R^(b), —NR^(d)—SO₂—R^(c), —CH₂—C(O)—NR^(a)R^(b),—C(O)—R^(d), —C(O)—OR^(d), or —C(O)—NR^(a)R^(b); R^(a) and R^(b) areeach independent and R^(a)s or R^(b)s when NR^(a)R^(b) exists plurallyare each independent, and they are hydrogen atom, C₁₋₄ alkyl (whereinthe alkyl is each independent and may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy), C₃₋₆ saturated carbocyclylgroup, or 4- to 6-membered saturated heterocyclyl group, wherein thesaturated carbocyclyl group and the saturated heterocyclyl group areeach independent and may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄ alkoxy, or alternatively,R^(a) and R^(b) may combine together with the nitrogen atom to whichthey attach to form a 4- to 6-membered nitrogen-containing saturatedheterocyclyl group, wherein the nitrogen-containing saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄ alkoxy; R^(c), where R^(c)sare each independent when existing plurally, is C₁₋₄ alkyl, C₃₋₆saturated carbocyclyl group, or 4- to 6-membered saturated heterocyclylgroup, wherein the alkyl, the saturated carbocyclyl group, and thesaturated heterocyclyl group are each independent and may be optionallysubstituted with the same or different 1 to 5 substituents selected fromthe group consisting of halogen atom, hydroxy, and C₁₋₄ alkoxy; R^(d),where R^(d)s are each independent when existing plurally, is hydrogenatom, C₁₋₄ alkyl, C₃₋₆ saturated carbocyclyl group, or 4- to 6-memberedsaturated heterocyclyl group, wherein the alkyl, the saturatedcarbocyclyl group, and the saturated heterocyclyl group are eachindependent and may be optionally substituted with the same or different1 to 5 substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy; X is nitrogen atom or —CR^(e)—; and R^(e) ishydrogen atom, halogen atom, cyano, C₁₋₆ alkyl, or C₁₋₆ alkoxy, whereinthe alkyl and the alkoxy may be optionally substituted with the same ordifferent 1 to 5 halogen atoms.
 2. The compound according to claim 1, ora pharmaceutically acceptable salt thereof, wherein R¹ and R² are eachindependently hydrogen atom or C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy, or alternatively, R¹ and R² combine together with the carbonatom to which they attach to form a cyclopropane ring or cyclobutanering.
 3. The compound according to claim 1, or a pharmaceuticallyacceptable salt thereof, wherein Ring A is benzene, naphthalene,pyridine, pyrimidine, pyrazine, thiophene, thiazole, isothiazole,oxazole, isoxazole, quinoline, isoquinoline, benzothiophene, benzofuran,indolizine, imidazopyridine, 1,3-benzodioxole, chromane,2,3-dihydrobenzofuran, 1,3-dihydroisobenzofuran, 2,3-dihydro-1H-indene,or 2,3-dihydro-1H-inden-1-one.
 4. The compound according to claim 1, ora pharmaceutically acceptable salt thereof, wherein R³ and R⁴ are eachindependently (1) hydrogen atom, (2) halogen atom, (3) cyano, (4)hydroxy, (5) C₁₋₄ alkyl optionally substituted with the same ordifferent 1 to 5 halogen atoms, (6) C₁₋₄ alkoxy optionally substitutedwith the same or different 1 to 5 halogen atoms, (7) C₃₋₆ cycloalkoxy,wherein the cycloalkoxy may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting of C₁₋₄alkyl and halogen atom, or (8) C₁₋₄ alkylthio optionally substitutedwith the same or different 1 to 5 halogen atoms.
 5. The compoundaccording to claim 1, or a pharmaceutically acceptable salt thereof,wherein R⁵ and R⁶ are each independently (1) hydrogen atom, (2) halogenatom, (3) cyano, (4) hydroxy, (5) C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy optionally substituted with the same or different 1 to 5 halogenatoms, (6) C₁₋₄ alkoxy, wherein the alkoxy may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms, (7) 4- to6-membered saturated heterocyclyl group, wherein the saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, or (8)—NR^(a)R^(b),—NR^(d)—C(O)—R^(c), —NR^(d)—C(O)—OR^(c), —NR^(d)—C(O)—NR^(a)R^(b),—NR^(d)—SO₂—R^(c), —CH₂—C(O)—NR^(a)R^(b), —C(O)—R^(d), —C(O)—OR^(d), or—C(O)—NR^(a)R^(b).
 6. The compound according to claim 1, or apharmaceutically acceptable salt thereof, wherein R^(a) and R^(b) areeach independent and R^(a)s or R^(b)s when NR^(a)R^(b) exists plurallyare each independent, and they are hydrogen atom or C₁₋₄ alkyl, whereinthe alkyl is each independent and may be optionally substituted with thesame or different 1 to 5 substituents selected from the group consistingof halogen atom, hydroxy, and C₁₋₄ alkoxy, or alternatively, R^(a) andR^(b) combine together with the nitrogen atom to which they attach toform a 4- to 6-membered nitrogen-containing saturated heterocyclylgroup, wherein the nitrogen-containing saturated heterocyclyl group maybe optionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, C₁₋₄ alkyl,and C₁₋₄ alkoxy.
 7. The compound according to claim 1, or apharmaceutically acceptable salt thereof, wherein R^(c), where R^(c)sare each independent when existing plurally, is C₁₋₄ alkyl or C₃₋₆saturated carbocyclyl group, wherein the alkyl and the saturatedcarbocyclyl group are each independent and may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy.
 8. The compoundaccording to claim 1, or a pharmaceutically acceptable salt thereof,wherein R^(d), where R^(d)s are each independent when existing plurally,is (1) hydrogen atom, (2) C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy, or (3) C₃₋₆ saturated carbocyclyl group, wherein the saturatedcarbocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy.
 9. The compound according toclaim 1, or a pharmaceutically acceptable salt thereof, wherein R^(e) is(1) hydrogen atom, (2) halogen atom, or (3) C₁₋₄ alkyl optionallysubstituted with the same or different 1 to 5 halogen atoms.
 10. Thecompound according to claim 33, or a pharmaceutically acceptable saltthereof, wherein R¹ and R² are each independently hydrogen atom, methyl,ethyl, isopropyl, cyclopropyl, methoxymethyl, hydroxymethyl,difluoromethyl, or trifluoromethyl, or alternatively, R¹ and R² combinetogether with the carbon atom to which they attach to form acyclopropane ring or a cyclobutane ring.
 11. The compound according toclaim 33, or a pharmaceutically acceptable salt thereof, wherein Ring Ais benzene, thiophene, pyridine, quinoline, or 1,3-benzodioxole.
 12. Thecompound according to claim 33, or a pharmaceutically acceptable saltthereof, wherein R³ and R⁴ are each independently (1) hydrogen atom, (2)halogen atom, (3) cyano, (4) C₁₋₄ alkyl optionally substituted with thesame or different 1 to 5 halogen atoms, or (5) C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms.
 13. Thecompound according to claim 33, or a pharmaceutically acceptable saltthereof, wherein R^(c), where R^(c)s are each independent when existingplurally, is C₁₋₄ alkyl optionally substituted with the same ordifferent 1 to 5 halogen atoms.
 14. The compound according to claim 33,or a pharmaceutically acceptable salt thereof, wherein R^(d), whereR^(d)s are each independent when existing plurally, is hydrogen atom orC₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms.
 15. The compound according to claim 33, or apharmaceutically acceptable salt thereof, wherein R^(d) and R^(d)s areeach independently (1) hydrogen atom, (2) halogen atom, (3) cyano, (4)hydroxy, (5) C₁₋₄ alkyl, wherein the alkyl may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms, (6) C₁₋₄alkoxy, wherein the alkoxy may be optionally substituted with the sameor different 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, (7) 4- to 6-membered saturatedheterocyclyl group, wherein the saturated heterocyclyl group may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy optionally substituted with the same or different 1 to 5 halogenatoms, or (8) —N^(a)R^(b).
 16. The compound according to claim 33, or apharmaceutically acceptable salt thereof, wherein R^(a) and R^(b) areeach independent and R^(a)s or R^(b)s when N^(a)R^(b) exists plurallyare each independent, and they are hydrogen atom or C₁₋₄ alkyl, whereinthe alkyl may be optionally substituted with the same or different 1 to3 substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy.
 17. The compound according to claim 33, or apharmaceutically acceptable salt thereof, wherein R^(e) is (1) hydrogenatom, (2) fluorine atom, or (3) C₁₋₄ alkyl optionally substituted withthe same or different 1 to 5 halogen atoms.
 18. The compound accordingto claim 1, or a pharmaceutically acceptable salt thereof, wherein R¹ ismethyl; R² is hydrogen atom; a6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one moiety has S-configurationat the 7-position; Ring A is benzene; R³ and R⁴ are each independentlyhydrogen atom, fluorine, chlorine, difluoromethyl, trifluoromethyl, ordifluoromethoxy; R⁵ and R⁶ are each independently hydrogen atom or —NH₂;and X is nitrogen atom or —CH—.
 19. The compound according to claim 1,or a pharmaceutically acceptable salt thereof, selected from thefollowing compounds:(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-3-(imidazo[1,2-a]pyrazin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[3-chloro-4-fluorophenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-5-[4-(difluoromethyl)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-5-(4-chloro-3-fluorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-5-(4-chlorophenyl)-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-5-[4-(difluoromethoxy)phenyl]-3-(imidazo[1,2-a]pyridin-6-yl)-7-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;and(7S)-3-(3-aminoimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one.20. The compound according to claim 1, or a pharmaceutically acceptablesalt thereof, selected from the following compounds:(7S)-3-(3-fluoroimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-7-methyl-3-(3-methylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;(7S)-3-(3-ethylimidazo[1,2-a]pyridin-6-yl)-7-methyl-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one;and(7S)-7-methyl-3-(3-propylimidazo[1,2-a]pyridin-6-yl)-5-[4-(trifluoromethyl)phenyl]-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one.21. A pharmaceutical composition comprising a compound according toclaim 1, or a pharmaceutically acceptable salt thereof.
 22. A method fortreating and/or preventing a disease involving Group II mGlu receptor,comprising administering a therapeutically effective amount of acompound according to claim 1, or a pharmaceutically acceptable saltthereof, to a patient in need thereof.
 23. The method according to claim22, wherein the Group II mGlu receptor is metabotropic glutamatereceptor subtype 2 (mGluR2).
 24. The method according to claim 22,wherein the disease involving Group II mGlu receptor is a psychiatricdisease or a neurodegenerative disease.
 25. The method according toclaim 24, wherein the psychiatric disease or neurodegenerative diseaseis major depressive disorder, depressive disorder, bipolar and relateddisorders, anxiety disorder, posttraumatic stress disorder,obsessive-compulsive disorder, acute stress disorder, schizophrenia,autism spectrum disorder, Alzheimer's disease, cognitive dysfunction,dementia, drug dependence, obesity, seizure, tremor, pain, or sleepdisorder. 26-28. (canceled)
 29. A pharmaceutical composition whichcomprises a compound according to claim 1, or a pharmaceuticallyacceptable salt thereof, and one or more agents selected fromtherapeutic agents for major depressive disorder, depressive disorder,bipolar and related disorders, anxiety disorder, posttraumatic stressdisorder, obsessive-compulsive disorder, acute stress disorder,schizophrenia, autism spectrum disorder, Alzheimer's disease, cognitivedysfunction, dementia, drug dependence, obesity, seizure, tremor, pain,or sleep disorder.
 30. A method for treating a psychiatric disease or aneurodegenerative disease, comprising administering a therapeuticallyeffective amount of a compound according to claim 1, or apharmaceutically acceptable salt thereof, in combination with one ormore antipsychotic drugs, to a patient in need thereof.
 31. A method ofpreparing a compound of Formula (1a):

or a pharmaceutically acceptable salt thereof, wherein R³ and R⁴ areeach independently hydrogen atom, halogen atom, C₁₋₆ alkyl, or C₁₋₄alkoxy, wherein the alkyl and the alkoxy are each independent and may beoptionally substituted with the same or different 1 to 5 halogen atoms;R⁵ and R⁶ are each independently hydrogen atom, halogen atom, C₁₋₆alkyl, or —NH₂; and X is nitrogen atom or —CH—, which comprises thefollowing steps: (step A1) reacting a compound of Formula (4a):

wherein PG is a protecting group such as tert-butoxycarbonyl group andbenzyloxycarbonyl group, and a compound of Formula (3):

wherein R⁷ is methyl or ethyl, under Mitsunobu condition to give acompound of Formula (6a):

wherein PG and R⁷ are as defined in this claim; (step A2) cyclizing thecompound of Formula (6a) in the presence of an acid or base to give acompound of Formula (7a):

(step A3) coupling the compound of Formula (7a) and a compound ofFormula (8a):

wherein R³ and R⁴ are as defined in this claim, and X¹ is iodine,bromine, or chlorine, in the presence of a transition metal catalyst togive a compound of Formula (9a):

wherein R³ and R⁴ are as defined in this claim; (step A4) reacting thecompound of Formula (9a) in the presence of a halogenating agent to givea compound of Formula (15a):

wherein R³, R⁴, and X¹ are as defined in this claim; and (step A5)coupling the compound of Formula (15a) and a compound of Formula (16):

or a salt thereof, wherein R⁵, R⁶, and X are as defined in this claim,and R^(A) is boronic acid or boronic acid ester, in the presence of atransition metal catalyst to give a compound of Formula (1a) or apharmaceutically acceptable salt thereof.
 32. A method of preparing acompound of Formula (1a):

or a pharmaceutically acceptable salt thereof, wherein R³ and R⁴ areeach independently hydrogen atom, halogen atom, C₁₋₆ alkyl, or C₁₋₄alkoxy, wherein the alkyl and the alkoxy are each independent and may beoptionally substituted with the same or different 1 to 5 halogen atoms;R⁵ and R⁶ are each independently hydrogen atom, halogen atom, C₁₋₆alkyl, or —NH₂; and X is nitrogen atom or —CH—, which comprises thefollowing steps: (step B1) coupling a compound of Formula (8a):

wherein R³ and R⁴ are as defined in this claim, and X¹ is iodine,bromine, or chlorine, with a compound of Formula (12a):

or a salt thereof, in the presence of a transition metal catalyst togive a compound of Formula (13a):

or a salt thereof, wherein R³ and R⁴ are as defined in this claim; (stepB2) reacting the compound of Formula (13a), or a salt thereof, and acompound of Formula (22):

or a salt thereof, wherein X is as defined in this claim, and R⁷ ismethyl or ethyl, under Mitsunobu condition to give a compound of Formula(23a):

or a salt thereof, wherein R³, R⁴, R⁷, and X¹ are as defined in thisclaim; (step B3) hydrolyzing the compound of Formula (23a), or a saltthereof, in the presence of an acid or base to give a compound ofFormula (24a):

or a salt thereof, wherein R³, R⁴, and X¹ are as defined in this claim;(step B4) cyclizing the compound of Formula (24a), or a salt thereof, inthe presence of an acid or base to give a compound of Formula (15a):

wherein R³, R⁴, and X¹ are as defined in this claim; and (step B5)coupling the compound of Formula (15a) and a compound of Formula (16):

or a salt thereof, wherein R⁵, R⁶, and X are as defined in this claim,and R^(A) is boronic acid or boronic acid ester, in the presence of atransition metal catalyst to give a compound of Formula (1a), or apharmaceutically acceptable salt thereof; wherein the step B3 and stepB4 may be replaced with one single step of the following step B6: (stepB6) cyclizing the compound of Formula (23a), or a salt thereof, in thepresence of an acid or base to give a compound of Formula (15a).
 33. Thecompound according to claim 1, or a pharmaceutically acceptable saltthereof, wherein R¹ and R² are each independently hydrogen atom or C₁₋₄alkyl, wherein the alkyl may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy, or alternatively, R¹ and R²combine together with the carbon atom to which they attach to form acyclopropane ring or cyclobutane ring; Ring A is benzene, naphthalene,pyridine, pyrimidine, pyrazine, thiophene, thiazole, isothiazole,oxazole, isoxazole, quinoline, isoquinoline, benzothiophene, benzofuran,indolizine, imidazopyridine, 1,3-benzodioxole, chromane,2,3-dihydrobenzofuran, 1,3-dihydroisobenzofuran, 2,3-dihydro-1H-indene,or 2,3-dihydro-1H-inden-1-one; R³ and R⁴ are each independently (1)hydrogen atom, (2) halogen atom, (3) cyano, (4) hydroxy, (5) C₁₋₄ alkyloptionally substituted with the same or different 1 to 5 halogen atoms,(6) C₁₋₄ alkoxy optionally substituted with the same or different 1 to 5halogen atoms, (7) C₃₋₆ cycloalkoxy, wherein the cycloalkoxy may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of C₁₋₄ alkyl and halogen atom, or(8) C₁₋₄ alkylthio optionally substituted with the same or different 1to 5 halogen atoms; R⁵ and R⁶ are each independently (1) hydrogen atom,(2) halogen atom, (3) cyano, (4) hydroxy, (5) C₁₋₄ alkyl, wherein thealkyl may be optionally substituted with the same or different 1 to 5substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy optionally substituted with the same ordifferent 1 to 5 halogen atoms, (6) C₁₋₄ alkoxy, wherein the alkoxy maybe optionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy optionally substituted with the same or different 1 to 5 halogenatoms, (7) 4- to 6-membered saturated heterocyclyl group, wherein thesaturated heterocyclyl group may be optionally substituted with the sameor different 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, or (8)—NR^(a)R^(b),—NR^(d)—C(O)—R^(c), —NR^(d)—C(O)—OR^(c), —NR^(d)—C(O)—NR^(a)R^(b),—NR^(d)—SO₂—R^(c), —CH₂—C(O)—NR^(a)R^(b), —C(O)—R^(d), —C(O)—OR^(d), or—C(O)—NR^(a)R^(b); R^(a) and R^(b) are each independent and R^(a)s orR^(b)s when NR^(a)R^(b) exists plurally are each independent, and theyare hydrogen atom or C₁₋₄ alkyl, wherein the alkyl is each independentand may be optionally substituted with the same or different 1 to 5substituents selected from the group consisting of halogen atom,hydroxy, and C₁₋₄ alkoxy, or alternatively, R^(a) and R^(b) combinetogether with the nitrogen atom to which they attach to form a 4- to6-membered nitrogen-containing saturated heterocyclyl group, wherein thenitrogen-containing saturated heterocyclyl group may be optionallysubstituted with the same or different 1 to 5 substituents selected fromthe group consisting of halogen atom, hydroxy, C₁₋₄ alkyl, and C₁₋₄alkoxy; R^(c), where R^(c)s are each independent when existing plurally,is C₁₋₄ alkyl or C₃₋₆ saturated carbocyclyl group, wherein the alkyl andthe saturated carbocyclyl group are each independent and may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy; R^(d), where R^(d)s are each independent when existing plurally,is (1) hydrogen atom, (2) C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy, or (3) C₃₋₆ saturated carbocyclyl group, wherein the saturatedcarbocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy; and R^(e) is (1) hydrogen atom,(2) halogen atom, or (3) C₁₋₄ alkyl optionally substituted with the sameor different 1 to 5 halogen atoms.
 34. The compound according to claim1, or a pharmaceutically acceptable salt thereof, wherein R¹ and R² areeach independently hydrogen atom, methyl, ethyl, isopropyl, cyclopropyl,methoxymethyl, hydroxymethyl, difluoromethyl, or trifluoromethyl, oralternatively, R¹ and R² combine together with the carbon atom to whichthey attach to form a cyclopropane ring or a cyclobutane ring; Ring A isbenzene, thiophene, pyridine, quinoline, or 1,3-benzodioxole; R³ and R⁴are each independently (1) hydrogen atom, (2) halogen atom, (3) cyano,(4) C₁₋₄ alkyl optionally substituted with the same or different 1 to 5halogen atoms, or (5) C₁₋₄ alkoxy optionally substituted with the sameor different 1 to 5 halogen atoms; R^(c), where R^(c)s are eachindependent when existing plurally, is C₁₋₄ alkyl optionally substitutedwith the same or different 1 to 5 halogen atoms; R^(d), where R^(d)s areeach independent when existing plurally, is hydrogen atom or C₁₋₄ alkyloptionally substituted with the same or different 1 to 5 halogen atoms;R⁵ and R⁶ are each independently (1) hydrogen atom, (2) halogen atom,(3) cyano, (4) hydroxy, (5) C₁₋₄ alkyl, wherein the alkyl may beoptionally substituted with the same or different 1 to 5 substituentsselected from the group consisting of halogen atom, hydroxy, and C₁₋₄alkoxy optionally substituted with the same or different 1 to 5 halogenatoms, (6) C₁₋₄ alkoxy, wherein the alkoxy may be optionally substitutedwith the same or different 1 to 5 substituents selected from the groupconsisting of halogen atom, hydroxy, and C₁₋₄ alkoxy optionallysubstituted with the same or different 1 to 5 halogen atoms, (7) 4- to6-membered saturated heterocyclyl group, wherein the saturatedheterocyclyl group may be optionally substituted with the same ordifferent 1 to 5 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy optionally substituted with thesame or different 1 to 5 halogen atoms, or (8)—NR^(a)R^(b); R^(a) andR^(b) are each independent and R^(a)s or R^(b)s when NR^(a)R^(b) existsplurally are each independent, and they are hydrogen atom or C₁₋₄ alkyl,wherein the alkyl may be optionally substituted with the same ordifferent 1 to 3 substituents selected from the group consisting ofhalogen atom, hydroxy, and C₁₋₄ alkoxy; and R^(e) is (1) hydrogen atom,(2) fluorine atom, or (3) C₁₋₄ alkyl optionally substituted with thesame or different 1 to 5 halogen atoms.
 35. The compound according toclaim 1, or a pharmaceutically acceptable salt thereof, wherein the6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one moiety has S-configurationat the 7-position.
 36. A pharmaceutical composition comprising acompound according to claim 18, or a pharmaceutically acceptable saltthereof.
 37. A pharmaceutical composition comprising a compoundaccording to claim 19, or a pharmaceutically acceptable salt thereof.38. A pharmaceutical composition comprising a compound according toclaim 20, or a pharmaceutically acceptable salt thereof.
 39. Apharmaceutical composition comprising a compound according to claim 33,or a pharmaceutically acceptable salt thereof.
 40. A pharmaceuticalcomposition comprising a compound according to claim 34, or apharmaceutically acceptable salt thereof.
 41. A pharmaceuticalcomposition comprising a compound according to claim 35, or apharmaceutically acceptable salt thereof.
 42. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 18, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 43. The method according to claim 42, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).44. The method according to claim 42, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 45. The method according to claim 44, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 46. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 19, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 47. The method according to claim 46, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).48. The method according to claim 46, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 49. The method according to claim 48, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 50. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 20, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 51. The method according to claim 50, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).52. The method according to claim 50, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 53. The method according to claim 52, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 54. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 33, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 55. The method according to claim 54, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).56. The method according to claim 54, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 57. The method according to claim 56, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 58. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 34, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 59. The method according to claim 58, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).60. The method according to claim 58, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 61. The method according to claim 60, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 62. A method for treatingand/or preventing a disease involving Group II mGlu receptor, comprisingadministering a therapeutically effective amount of a compound accordingto claim 35, or a pharmaceutically acceptable salt thereof, to a patientin need thereof.
 63. The method according to claim 62, wherein the GroupII mGlu receptor is metabotropic glutamate receptor subtype 2 (mGuR2).64. The method according to claim 62, wherein the disease involvingGroup II mGlu receptor is a psychiatric disease or a neurodegenerativedisease.
 65. The method according to claim 64, wherein the psychiatricdisease or neurodegenerative disease is major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 66. A pharmaceuticalcomposition which comprises a compound according to claim 18, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 67. A pharmaceuticalcomposition which comprises a compound according to claim 19, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 68. A pharmaceuticalcomposition which comprises a compound according to claim 20, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 69. A pharmaceuticalcomposition which comprises a compound according to claim 33, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 70. A pharmaceuticalcomposition which comprises a compound according to claim 34, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 71. A pharmaceuticalcomposition which comprises a compound according to claim 35, or apharmaceutically acceptable salt thereof, and one or more agentsselected from therapeutic agents for major depressive disorder,depressive disorder, bipolar and related disorders, anxiety disorder,posttraumatic stress disorder, obsessive-compulsive disorder, acutestress disorder, schizophrenia, autism spectrum disorder, Alzheimer'sdisease, cognitive dysfunction, dementia, drug dependence, obesity,seizure, tremor, pain, or sleep disorder.
 72. A method for treating apsychiatric disease or a neurodegenerative disease, comprisingadministering a therapeutically effective amount of a compound accordingto claim 18, or a pharmaceutically acceptable salt thereof, incombination with one or more antipsychotic drugs, to a patient in needthereof.
 73. A method for treating a psychiatric disease or aneurodegenerative disease, comprising administering a therapeuticallyeffective amount of a compound according to claim 19, or apharmaceutically acceptable salt thereof, in combination with one ormore antipsychotic drugs, to a patient in need thereof.
 74. A method fortreating a psychiatric disease or a neurodegenerative disease,comprising administering a therapeutically effective amount of acompound according to claim 20, or a pharmaceutically acceptable saltthereof, in combination with one or more antipsychotic drugs, to apatient in need thereof.
 75. A method for treating a psychiatric diseaseor a neurodegenerative disease, comprising administering atherapeutically effective amount of a compound according to claim 33, ora pharmaceutically acceptable salt thereof, in combination with one ormore antipsychotic drugs, to a patient in need thereof.
 76. A method fortreating a psychiatric disease or a neurodegenerative disease,comprising administering a therapeutically effective amount of acompound according to claim 34, or a pharmaceutically acceptable saltthereof, in combination with one or more antipsychotic drugs, to apatient in need thereof.
 77. A method for treating a psychiatric diseaseor a neurodegenerative disease, comprising administering atherapeutically effective amount of a compound according to claim 35, ora pharmaceutically acceptable salt thereof, in combination with one ormore antipsychotic drugs, to a patient in need thereof.